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 $69.41   9.237%   $75.8214   $75.82   $75.80   $75.80  
  Purchase #2 $77.45   13.818%   $88.152   $88.15   $88.15   $88.20  
  Purchase #3 $152.72   4.349%   $159.3618   $159.36   $159.35   $159.40  
  Purchase #4 $125.26   3.258%   $129.341   $129.34   $129.35   $129.30  
  Purchase #5 $92.77   5.350%   $97.7332   $97.73   $97.75   $97.70  
  Purchase #6 $11.69   3.659%   $12.1177   $12.12   $12.10   $12.10  
  Purchase #7 $32.57   8.200%   $35.2407   $35.24   $35.25   $35.20  
  7 purchase totals = $561.87       $597.7678   $597.76   $597.75   $597.70