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 $245.95   7.553%   $264.5266   $264.53   $264.55   $264.50  
  Purchase #2 $44.37   4.458%   $46.348   $46.35   $46.35   $46.30  
  Purchase #3 $112.67   11.469%   $125.5921   $125.59   $125.60   $125.60  
  Purchase #4 $6.80   11.811%   $7.6031   $7.60   $7.60   $7.60  
  Purchase #5 $98.38   3.677%   $101.9974   $102.00   $102.00   $102.00  
  Purchase #6 $96.39   6.259%   $102.4231   $102.42   $102.40   $102.40  
  Purchase #7 $133.46   9.801%   $146.5404   $146.54   $146.55   $146.50  
  7 purchase totals = $738.02       $795.0307   $795.03   $795.05   $794.90