Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $214.70   10.789%   $237.864   $237.86   $237.85   $237.90  
  Purchase #2 $185.63   8.258%   $200.9593   $200.96   $200.95   $201.00  
  Purchase #3 $104.39   9.590%   $114.401   $114.40   $114.40   $114.40  
  Purchase #4 $230.54   4.522%   $240.965   $240.97   $240.95   $241.00  
  Purchase #5 $156.74   10.648%   $173.4297   $173.43   $173.45   $173.40  
  Purchase #6 $41.42   6.653%   $44.1757   $44.18   $44.20   $44.20  
  Purchase #7 $235.38   12.608%   $265.0567   $265.06   $265.05   $265.10  
  7 purchase totals = $1,168.80       $1,276.8514   $1,276.86   $1,276.85   $1,277.00