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 $119.66   4.406%   $124.9322   $124.93   $124.95   $124.90  
  Purchase #2 $240.41   12.285%   $269.9444   $269.94   $269.95   $269.90  
  Purchase #3 $102.73   8.653%   $111.6192   $111.62   $111.60   $111.60  
  Purchase #4 $125.56   5.498%   $132.4633   $132.46   $132.45   $132.50  
  Purchase #5 $204.82   9.577%   $224.4356   $224.44   $224.45   $224.40  
  Purchase #6 $13.70   7.142%   $14.6785   $14.68   $14.70   $14.70  
  Purchase #7 $148.35   8.228%   $160.5562   $160.56   $160.55   $160.60  
  7 purchase totals = $955.23       $1,038.6294   $1,038.63   $1,038.65   $1,038.60