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 $228.95   11.486%   $255.2472   $255.25   $255.25   $255.20  
  Purchase #2 $68.51   5.619%   $72.3596   $72.36   $72.35   $72.40  
  Purchase #3 $219.86   5.228%   $231.3543   $231.35   $231.35   $231.40  
  Purchase #4 $220.78   13.674%   $250.9695   $250.97   $250.95   $251.00  
  Purchase #5 $167.84   8.767%   $182.5545   $182.55   $182.55   $182.60  
  Purchase #6 $210.42   3.673%   $218.1487   $218.15   $218.15   $218.10  
  Purchase #7 $227.59   7.254%   $244.0994   $244.10   $244.10   $244.10  
  7 purchase totals = $1,343.95       $1,454.7332   $1,454.73   $1,454.70   $1,454.80