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 $57.32   10.620%   $63.4074   $63.41   $63.40   $63.40  
  Purchase #2 $74.92   13.826%   $85.2784   $85.28   $85.30   $85.30  
  Purchase #3 $187.72   5.129%   $197.3482   $197.35   $197.35   $197.30  
  Purchase #4 $244.55   4.713%   $256.0756   $256.08   $256.10   $256.10  
  Purchase #5 $92.97   5.804%   $98.366   $98.37   $98.35   $98.40  
  Purchase #6 $22.29   7.746%   $24.0166   $24.02   $24.00   $24.00  
  Purchase #7 $46.42   4.130%   $48.3371   $48.34   $48.35   $48.30  
  7 purchase totals = $726.19       $772.8293   $772.85   $772.85   $772.80