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 $161.38   13.114%   $182.5434   $182.54   $182.55   $182.50  
  Purchase #2 $184.78   13.626%   $209.9581   $209.96   $209.95   $210.00  
  Purchase #3 $48.28   5.560%   $50.9644   $50.96   $50.95   $51.00  
  Purchase #4 $26.34   12.567%   $29.6501   $29.65   $29.65   $29.70  
  Purchase #5 $166.71   12.701%   $187.8838   $187.88   $187.90   $187.90  
  Purchase #6 $217.32   13.230%   $246.0714   $246.07   $246.05   $246.10  
  Purchase #7 $237.42   5.518%   $250.5208   $250.52   $250.50   $250.50  
  7 purchase totals = $1,042.23       $1,157.5920   $1,157.58   $1,157.55   $1,157.70