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 $62.76   7.493%   $67.4626   $67.46   $67.45   $67.50  
  Purchase #2 $209.43   8.591%   $227.4221   $227.42   $227.40   $227.40  
  Purchase #3 $46.33   10.556%   $51.2206   $51.22   $51.20   $51.20  
  Purchase #4 $140.51   12.158%   $157.5932   $157.59   $157.60   $157.60  
  Purchase #5 $138.43   8.119%   $149.6691   $149.67   $149.65   $149.70  
  Purchase #6 $146.50   12.410%   $164.6807   $164.68   $164.70   $164.70  
  Purchase #7 $236.96   12.448%   $266.4568   $266.46   $266.45   $266.50  
  7 purchase totals = $980.92       $1,084.5051   $1,084.50   $1,084.45   $1,084.60