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 $49.60   3.348%   $51.2606   $51.26   $51.25   $51.30  
  Purchase #2 $186.62   4.812%   $195.6002   $195.60   $195.60   $195.60  
  Purchase #3 $132.93   8.623%   $144.3926   $144.39   $144.40   $144.40  
  Purchase #4 $125.61   12.624%   $141.467   $141.47   $141.45   $141.50  
  Purchase #5 $159.90   6.501%   $170.2951   $170.30   $170.30   $170.30  
  Purchase #6 $236.42   12.324%   $265.5564   $265.56   $265.55   $265.60  
  Purchase #7 $6.75   4.267%   $7.038   $7.04   $7.05   $7.00  
  7 purchase totals = $897.83       $975.6099   $975.62   $975.60   $975.70