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 $232.70   12.166%   $261.0103   $261.01   $261.00   $261.00  
  Purchase #2 $159.33   9.603%   $174.6305   $174.63   $174.65   $174.60  
  Purchase #3 $226.36   4.594%   $236.759   $236.76   $236.75   $236.80  
  Purchase #4 $151.40   12.779%   $170.7474   $170.75   $170.75   $170.70  
  Purchase #5 $215.53   8.267%   $233.3479   $233.35   $233.35   $233.30  
  Purchase #6 $89.79   4.603%   $93.923   $93.92   $93.90   $93.90  
  Purchase #7 $151.67   12.862%   $171.1778   $171.18   $171.20   $171.20  
  7 purchase totals = $1,226.78       $1,341.5959   $1,341.60   $1,341.60   $1,341.50