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 $201.50   4.811%   $211.1942   $211.19   $211.20   $211.20  
  Purchase #2 $231.87   12.858%   $261.6838   $261.68   $261.70   $261.70  
  Purchase #3 $62.41   11.402%   $69.526   $69.53   $69.55   $69.50  
  Purchase #4 $68.30   13.258%   $77.3552   $77.36   $77.35   $77.40  
  Purchase #5 $215.27   7.444%   $231.2947   $231.29   $231.30   $231.30  
  Purchase #6 $248.55   4.795%   $260.468   $260.47   $260.45   $260.50  
  Purchase #7 $106.64   12.410%   $119.874   $119.87   $119.85   $119.90  
  7 purchase totals = $1,134.54       $1,231.3959   $1,231.39   $1,231.40   $1,231.50