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 $175.49   8.817%   $190.963   $190.96   $190.95   $191.00  
  Purchase #2 $58.50   5.480%   $61.7058   $61.71   $61.70   $61.70  
  Purchase #3 $126.68   7.634%   $136.3508   $136.35   $136.35   $136.40  
  Purchase #4 $160.53   5.862%   $169.9403   $169.94   $169.95   $169.90  
  Purchase #5 $42.72   6.775%   $45.6143   $45.61   $45.60   $45.60  
  Purchase #6 $87.91   3.134%   $90.6651   $90.67   $90.65   $90.70  
  Purchase #7 $205.59   12.318%   $230.9146   $230.91   $230.90   $230.90  
  7 purchase totals = $857.42       $926.1539   $926.15   $926.10   $926.20