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 $190.35   6.109%   $201.9785   $201.98   $202.00   $202.00  
  Purchase #2 $210.94   11.725%   $235.6727   $235.67   $235.65   $235.70  
  Purchase #3 $140.54   12.719%   $158.4153   $158.42   $158.40   $158.40  
  Purchase #4 $11.95   10.646%   $13.2222   $13.22   $13.20   $13.20  
  Purchase #5 $129.48   6.869%   $138.374   $138.37   $138.35   $138.40  
  Purchase #6 $61.77   4.260%   $64.4014   $64.40   $64.40   $64.40  
  Purchase #7 $92.28   3.391%   $95.4092   $95.41   $95.40   $95.40  
  7 purchase totals = $837.31       $907.4733   $907.47   $907.40   $907.50