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 $35.72   6.245%   $37.9507   $37.95   $37.95   $38.00  
  Purchase #2 $88.45   6.617%   $94.3027   $94.30   $94.30   $94.30  
  Purchase #3 $219.64   8.378%   $238.0414   $238.04   $238.05   $238.00  
  Purchase #4 $69.39   7.497%   $74.5922   $74.59   $74.60   $74.60  
  Purchase #5 $225.29   7.359%   $241.8691   $241.87   $241.85   $241.90  
  Purchase #6 $214.46   13.238%   $242.8502   $242.85   $242.85   $242.90  
  Purchase #7 $60.71   9.493%   $66.4732   $66.47   $66.45   $66.50  
  7 purchase totals = $913.66       $996.0795   $996.07   $996.05   $996.20