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 $118.80   5.540%   $125.3815   $125.38   $125.40   $125.40  
  Purchase #2 $172.87   10.522%   $191.0594   $191.06   $191.05   $191.10  
  Purchase #3 $186.43   6.117%   $197.8339   $197.83   $197.85   $197.80  
  Purchase #4 $101.28   4.294%   $105.629   $105.63   $105.65   $105.60  
  Purchase #5 $143.38   10.394%   $158.2829   $158.28   $158.30   $158.30  
  Purchase #6 $43.33   12.478%   $48.7367   $48.74   $48.75   $48.70  
  Purchase #7 $200.78   6.380%   $213.5898   $213.59   $213.60   $213.60  
  7 purchase totals = $966.87       $1,040.5132   $1,040.51   $1,040.60   $1,040.50