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 $57.67   6.254%   $61.2767   $61.28   $61.30   $61.30  
  Purchase #2 $170.26   4.275%   $177.5386   $177.54   $177.55   $177.50  
  Purchase #3 $81.63   4.494%   $85.2985   $85.30   $85.30   $85.30  
  Purchase #4 $59.78   12.700%   $67.3721   $67.37   $67.35   $67.40  
  Purchase #5 $183.26   7.554%   $197.1035   $197.10   $197.10   $197.10  
  Purchase #6 $93.73   6.425%   $99.7522   $99.75   $99.75   $99.80  
  Purchase #7 $46.86   4.400%   $48.9218   $48.92   $48.90   $48.90  
  7 purchase totals = $693.19       $737.2634   $737.26   $737.25   $737.30