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 $231.93   12.548%   $261.0326   $261.03   $261.05   $261.00  
  Purchase #2 $213.43   13.164%   $241.5259   $241.53   $241.55   $241.50  
  Purchase #3 $18.31   5.389%   $19.2967   $19.30   $19.30   $19.30  
  Purchase #4 $227.63   10.152%   $250.739   $250.74   $250.75   $250.70  
  Purchase #5 $226.56   9.496%   $248.0741   $248.07   $248.05   $248.10  
  Purchase #6 $141.80   12.821%   $159.9802   $159.98   $160.00   $160.00  
  Purchase #7 $28.36   9.138%   $30.9515   $30.95   $30.95   $31.00  
  7 purchase totals = $1,088.02       $1,211.6000   $1,211.60   $1,211.65   $1,211.60