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 $227.84   11.481%   $253.9983   $254.00   $254.00   $254.00  
  Purchase #2 $113.94   5.249%   $119.9207   $119.92   $119.90   $119.90  
  Purchase #3 $38.73   11.356%   $43.1282   $43.13   $43.15   $43.10  
  Purchase #4 $133.37   7.349%   $143.1714   $143.17   $143.15   $143.20  
  Purchase #5 $39.38   10.443%   $43.4925   $43.49   $43.50   $43.50  
  Purchase #6 $213.64   6.294%   $227.0865   $227.09   $227.10   $227.10  
  Purchase #7 $173.61   5.277%   $182.7714   $182.77   $182.75   $182.80  
  7 purchase totals = $940.51       $1,013.5690   $1,013.57   $1,013.55   $1,013.60