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 $194.74   10.380%   $214.954   $214.95   $214.95   $215.00  
  Purchase #2 $120.79   6.765%   $128.9614   $128.96   $128.95   $129.00  
  Purchase #3 $48.62   10.682%   $53.8136   $53.81   $53.80   $53.80  
  Purchase #4 $227.46   4.411%   $237.4933   $237.49   $237.50   $237.50  
  Purchase #5 $217.67   5.410%   $229.4459   $229.45   $229.45   $229.40  
  Purchase #6 $51.99   11.567%   $58.0037   $58.00   $58.00   $58.00  
  Purchase #7 $223.71   11.435%   $249.2912   $249.29   $249.30   $249.30  
  7 purchase totals = $1,084.98       $1,171.9631   $1,171.95   $1,171.95   $1,172.00