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 $41.73   3.747%   $43.2936   $43.29   $43.30   $43.30  
  Purchase #2 $209.82   3.524%   $217.2141   $217.21   $217.20   $217.20  
  Purchase #3 $178.64   3.528%   $184.9424   $184.94   $184.95   $184.90  
  Purchase #4 $38.96   5.706%   $41.1831   $41.18   $41.20   $41.20  
  Purchase #5 $88.63   7.710%   $95.4634   $95.46   $95.45   $95.50  
  Purchase #6 $186.40   13.785%   $212.0952   $212.10   $212.10   $212.10  
  Purchase #7 $119.45   10.541%   $132.0412   $132.04   $132.05   $132.00  
  7 purchase totals = $863.63       $926.2330   $926.22   $926.25   $926.20