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 $69.44   6.179%   $73.7307   $73.73   $73.75   $73.70  
  Purchase #2 $92.47   9.833%   $101.5626   $101.56   $101.55   $101.60  
  Purchase #3 $157.37   12.187%   $176.5487   $176.55   $176.55   $176.50  
  Purchase #4 $112.33   5.766%   $118.8069   $118.81   $118.80   $118.80  
  Purchase #5 $43.40   11.443%   $48.3663   $48.37   $48.35   $48.40  
  Purchase #6 $123.65   13.241%   $140.0225   $140.02   $140.00   $140.00  
  Purchase #7 $12.63   7.775%   $13.612   $13.61   $13.60   $13.60  
  7 purchase totals = $611.29       $672.6497   $672.65   $672.60   $672.60