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 $190.32   8.376%   $206.2612   $206.26   $206.25   $206.30  
  Purchase #2 $180.25   9.426%   $197.2404   $197.24   $197.25   $197.20  
  Purchase #3 $195.77   5.696%   $206.9211   $206.92   $206.90   $206.90  
  Purchase #4 $48.68   9.850%   $53.475   $53.48   $53.50   $53.50  
  Purchase #5 $105.94   8.825%   $115.2892   $115.29   $115.30   $115.30  
  Purchase #6 $44.97   5.498%   $47.4425   $47.44   $47.45   $47.40  
  Purchase #7 $125.33   6.563%   $133.5554   $133.56   $133.55   $133.60  
  7 purchase totals = $891.26       $960.1848   $960.19   $960.20   $960.20