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 $53.35   9.226%   $58.2721   $58.27   $58.25   $58.30  
  Purchase #2 $90.72   7.251%   $97.2981   $97.30   $97.30   $97.30  
  Purchase #3 $56.51   6.427%   $60.1419   $60.14   $60.15   $60.10  
  Purchase #4 $93.80   6.347%   $99.7535   $99.75   $99.75   $99.80  
  Purchase #5 $62.89   9.558%   $68.901   $68.90   $68.90   $68.90  
  Purchase #6 $27.88   8.853%   $30.3482   $30.35   $30.35   $30.30  
  Purchase #7 $172.93   4.191%   $180.1775   $180.18   $180.20   $180.20  
  7 purchase totals = $558.08       $594.8923   $594.89   $594.90   $594.90