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 $224.86   5.733%   $237.7512   $237.75   $237.75   $237.80  
  Purchase #2 $129.31   4.648%   $135.3203   $135.32   $135.30   $135.30  
  Purchase #3 $56.50   3.648%   $58.5611   $58.56   $58.55   $58.60  
  Purchase #4 $60.30   8.401%   $65.3658   $65.37   $65.35   $65.40  
  Purchase #5 $24.52   13.218%   $27.7611   $27.76   $27.75   $27.80  
  Purchase #6 $172.75   5.826%   $182.8144   $182.81   $182.80   $182.80  
  Purchase #7 $50.85   10.266%   $56.0703   $56.07   $56.05   $56.10  
  7 purchase totals = $719.09       $763.6442   $763.64   $763.55   $763.80