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 $205.76   10.790%   $227.9615   $227.96   $227.95   $228.00  
  Purchase #2 $228.78   3.482%   $236.7461   $236.75   $236.75   $236.70  
  Purchase #3 $33.56   8.656%   $36.465   $36.47   $36.45   $36.50  
  Purchase #4 $151.54   7.189%   $162.4342   $162.43   $162.45   $162.40  
  Purchase #5 $244.37   5.110%   $256.8573   $256.86   $256.85   $256.90  
  Purchase #6 $200.86   7.146%   $215.2135   $215.21   $215.20   $215.20  
  Purchase #7 $136.94   13.296%   $155.1475   $155.15   $155.15   $155.10  
  7 purchase totals = $1,201.81       $1,290.8251   $1,290.83   $1,290.80   $1,290.80