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 $210.34   7.460%   $226.0314   $226.03   $226.05   $226.00  
  Purchase #2 $96.39   4.351%   $100.5839   $100.58   $100.60   $100.60  
  Purchase #3 $107.80   3.733%   $111.8242   $111.82   $111.80   $111.80  
  Purchase #4 $124.95   4.640%   $130.7477   $130.75   $130.75   $130.70  
  Purchase #5 $236.26   6.858%   $252.4627   $252.46   $252.45   $252.50  
  Purchase #6 $60.91   3.488%   $63.0345   $63.03   $63.05   $63.00  
  Purchase #7 $140.28   7.306%   $150.5289   $150.53   $150.55   $150.50  
  7 purchase totals = $976.93       $1,035.2133   $1,035.20   $1,035.25   $1,035.10