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 $55.37   13.694%   $62.9524   $62.95   $62.95   $63.00  
  Purchase #2 $49.34   8.165%   $53.3686   $53.37   $53.35   $53.40  
  Purchase #3 $176.37   4.527%   $184.3543   $184.35   $184.35   $184.40  
  Purchase #4 $205.45   12.192%   $230.4985   $230.50   $230.50   $230.50  
  Purchase #5 $175.58   6.352%   $186.7328   $186.73   $186.75   $186.70  
  Purchase #6 $91.97   10.629%   $101.7455   $101.75   $101.75   $101.70  
  Purchase #7 $168.79   13.474%   $191.5328   $191.53   $191.55   $191.50  
  7 purchase totals = $922.87       $1,011.1849   $1,011.18   $1,011.20   $1,011.20