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 $111.49   12.679%   $125.6258   $125.63   $125.65   $125.60  
  Purchase #2 $182.50   4.824%   $191.3038   $191.30   $191.30   $191.30  
  Purchase #3 $139.93   3.506%   $144.8359   $144.84   $144.85   $144.80  
  Purchase #4 $105.26   6.682%   $112.2935   $112.29   $112.30   $112.30  
  Purchase #5 $89.79   8.353%   $97.2902   $97.29   $97.30   $97.30  
  Purchase #6 $17.84   6.647%   $19.0258   $19.03   $19.05   $19.00  
  Purchase #7 $58.49   9.753%   $64.1945   $64.19   $64.20   $64.20  
  7 purchase totals = $705.30       $754.5695   $754.57   $754.65   $754.50