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 $211.34   12.124%   $236.9629   $236.96   $236.95   $237.00  
  Purchase #2 $215.71   10.365%   $238.0683   $238.07   $238.05   $238.10  
  Purchase #3 $216.47   12.105%   $242.6737   $242.67   $242.65   $242.70  
  Purchase #4 $174.57   5.331%   $183.8763   $183.88   $183.90   $183.90  
  Purchase #5 $40.47   7.331%   $43.4369   $43.44   $43.45   $43.40  
  Purchase #6 $201.96   5.169%   $212.3993   $212.40   $212.40   $212.40  
  Purchase #7 $148.41   5.188%   $156.1095   $156.11   $156.10   $156.10  
  7 purchase totals = $1,208.93       $1,313.5269   $1,313.53   $1,313.50   $1,313.60