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 $68.82   6.494%   $73.2892   $73.29   $73.30   $73.30  
  Purchase #2 $101.57   12.213%   $113.9747   $113.97   $113.95   $114.00  
  Purchase #3 $76.50   9.795%   $83.9932   $83.99   $84.00   $84.00  
  Purchase #4 $224.39   3.135%   $231.4246   $231.42   $231.40   $231.40  
  Purchase #5 $129.89   12.235%   $145.782   $145.78   $145.80   $145.80  
  Purchase #6 $18.93   12.485%   $21.2934   $21.29   $21.30   $21.30  
  Purchase #7 $59.52   4.434%   $62.1591   $62.16   $62.15   $62.20  
  7 purchase totals = $679.62       $731.9162   $731.90   $731.90   $732.00