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 $63.52   8.149%   $68.6962   $68.70   $68.70   $68.70  
  Purchase #2 $51.87   10.350%   $57.2385   $57.24   $57.25   $57.20  
  Purchase #3 $221.63   4.756%   $232.1707   $232.17   $232.15   $232.20  
  Purchase #4 $231.76   7.430%   $248.9798   $248.98   $249.00   $249.00  
  Purchase #5 $146.68   13.293%   $166.1782   $166.18   $166.20   $166.20  
  Purchase #6 $33.64   11.461%   $37.4955   $37.50   $37.50   $37.50  
  Purchase #7 $13.66   7.215%   $14.6456   $14.65   $14.65   $14.60  
  7 purchase totals = $762.76       $825.4045   $825.42   $825.45   $825.40