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 $246.37   6.538%   $262.4777   $262.48   $262.50   $262.50  
  Purchase #2 $69.49   10.104%   $76.5113   $76.51   $76.50   $76.50  
  Purchase #3 $93.58   8.350%   $101.3939   $101.39   $101.40   $101.40  
  Purchase #4 $67.45   5.673%   $71.2764   $71.28   $71.30   $71.30  
  Purchase #5 $26.27   3.766%   $27.2593   $27.26   $27.25   $27.30  
  Purchase #6 $159.86   8.291%   $173.114   $173.11   $173.10   $173.10  
  Purchase #7 $23.99   4.539%   $25.0789   $25.08   $25.10   $25.10  
  7 purchase totals = $687.01       $737.1115   $737.11   $737.15   $737.20