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 $222.50   10.656%   $246.2096   $246.21   $246.20   $246.20  
  Purchase #2 $130.98   4.249%   $136.5453   $136.55   $136.55   $136.50  
  Purchase #3 $83.82   13.499%   $95.1349   $95.13   $95.15   $95.10  
  Purchase #4 $75.56   12.793%   $85.2264   $85.23   $85.25   $85.20  
  Purchase #5 $96.96   8.528%   $105.2287   $105.23   $105.25   $105.20  
  Purchase #6 $76.78   12.828%   $86.6293   $86.63   $86.65   $86.60  
  Purchase #7 $238.43   8.593%   $258.9183   $258.92   $258.90   $258.90  
  7 purchase totals = $925.03       $1,013.8925   $1,013.90   $1,013.95   $1,013.70