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 $38.81   5.628%   $40.9942   $40.99   $41.00   $41.00  
  Purchase #2 $55.66   13.184%   $62.9982   $63.00   $63.00   $63.00  
  Purchase #3 $86.42   8.757%   $93.9878   $93.99   $94.00   $94.00  
  Purchase #4 $227.38   6.840%   $242.9328   $242.93   $242.95   $242.90  
  Purchase #5 $93.67   12.307%   $105.198   $105.20   $105.20   $105.20  
  Purchase #6 $140.97   13.309%   $159.7317   $159.73   $159.75   $159.70  
  Purchase #7 $242.73   3.441%   $251.0823   $251.08   $251.10   $251.10  
  7 purchase totals = $885.64       $956.9250   $956.92   $957.00   $956.90