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 $210.62   13.284%   $238.5988   $238.60   $238.60   $238.60  
  Purchase #2 $118.97   4.137%   $123.8918   $123.89   $123.90   $123.90  
  Purchase #3 $156.32   13.441%   $177.331   $177.33   $177.35   $177.30  
  Purchase #4 $154.89   3.865%   $160.8765   $160.88   $160.90   $160.90  
  Purchase #5 $185.43   11.593%   $206.9269   $206.93   $206.95   $206.90  
  Purchase #6 $244.89   6.350%   $260.4405   $260.44   $260.45   $260.40  
  Purchase #7 $250.80   3.707%   $260.0972   $260.10   $260.10   $260.10  
  7 purchase totals = $1,321.92       $1,428.1627   $1,428.17   $1,428.25   $1,428.10