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 $195.55   5.814%   $206.9193   $206.92   $206.90   $206.90  
  Purchase #2 $69.54   12.491%   $78.2262   $78.23   $78.25   $78.20  
  Purchase #3 $235.67   10.707%   $260.9032   $260.90   $260.90   $260.90  
  Purchase #4 $230.82   11.856%   $258.186   $258.19   $258.20   $258.20  
  Purchase #5 $53.72   11.606%   $59.9547   $59.95   $59.95   $60.00  
  Purchase #6 $22.54   7.341%   $24.1947   $24.19   $24.20   $24.20  
  Purchase #7 $172.56   3.590%   $178.7549   $178.75   $178.75   $178.80  
  7 purchase totals = $980.40       $1,067.1390   $1,067.13   $1,067.15   $1,067.20