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   13.689%   $78.9115   $78.91   $78.90   $78.90  
  Purchase #2 $244.47   12.522%   $275.0825   $275.08   $275.10   $275.10  
  Purchase #3 $205.48   4.773%   $215.2876   $215.29   $215.30   $215.30  
  Purchase #4 $93.92   8.697%   $102.0882   $102.09   $102.10   $102.10  
  Purchase #5 $25.83   10.503%   $28.5429   $28.54   $28.55   $28.50  
  Purchase #6 $59.35   8.449%   $64.3645   $64.36   $64.35   $64.40  
  Purchase #7 $195.75   8.428%   $212.2478   $212.25   $212.25   $212.20  
  7 purchase totals = $894.21       $976.5250   $976.52   $976.55   $976.50