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 $86.61   12.326%   $97.2855   $97.29   $97.30   $97.30  
  Purchase #2 $120.57   4.863%   $126.4333   $126.43   $126.45   $126.40  
  Purchase #3 $97.29   9.247%   $106.2864   $106.29   $106.30   $106.30  
  Purchase #4 $187.59   8.785%   $204.0698   $204.07   $204.05   $204.10  
  Purchase #5 $104.28   8.704%   $113.3565   $113.36   $113.35   $113.40  
  Purchase #6 $54.57   12.298%   $61.281   $61.28   $61.30   $61.30  
  Purchase #7 $143.36   11.452%   $159.7776   $159.78   $159.80   $159.80  
  7 purchase totals = $794.27       $868.4901   $868.50   $868.55   $868.60