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 $243.71   4.202%   $253.9507   $253.95   $253.95   $254.00  
  Purchase #2 $166.31   13.230%   $188.3128   $188.31   $188.30   $188.30  
  Purchase #3 $78.36   3.451%   $81.0642   $81.06   $81.05   $81.10  
  Purchase #4 $70.66   3.731%   $73.2963   $73.30   $73.30   $73.30  
  Purchase #5 $231.34   12.842%   $261.0487   $261.05   $261.05   $261.00  
  Purchase #6 $141.94   12.332%   $159.444   $159.44   $159.45   $159.40  
  Purchase #7 $5.47   4.829%   $5.7341   $5.73   $5.75   $5.70  
  7 purchase totals = $937.79       $1,022.8508   $1,022.84   $1,022.85   $1,022.80