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 $243.53   5.310%   $256.4614   $256.46   $256.45   $256.50  
  Purchase #2 $56.55   7.357%   $60.7104   $60.71   $60.70   $60.70  
  Purchase #3 $189.92   3.135%   $195.874   $195.87   $195.85   $195.90  
  Purchase #4 $210.85   11.386%   $234.8574   $234.86   $234.85   $234.90  
  Purchase #5 $248.25   5.701%   $262.4027   $262.40   $262.40   $262.40  
  Purchase #6 $210.53   3.523%   $217.947   $217.95   $217.95   $217.90  
  Purchase #7 $132.72   11.696%   $148.2429   $148.24   $148.25   $148.20  
  7 purchase totals = $1,292.35       $1,376.4958   $1,376.49   $1,376.45   $1,376.50