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 $230.85   5.250%   $242.9696   $242.97   $242.95   $243.00  
  Purchase #2 $112.79   9.582%   $123.5975   $123.60   $123.60   $123.60  
  Purchase #3 $64.29   13.615%   $73.0431   $73.04   $73.05   $73.00  
  Purchase #4 $224.29   5.341%   $236.2693   $236.27   $236.25   $236.30  
  Purchase #5 $156.69   12.513%   $176.2966   $176.30   $176.30   $176.30  
  Purchase #6 $35.63   8.133%   $38.5278   $38.53   $38.55   $38.50  
  Purchase #7 $59.77   3.128%   $61.6396   $61.64   $61.65   $61.60  
  7 purchase totals = $884.31       $952.3435   $952.35   $952.35   $952.30