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 $58.49   13.104%   $66.1545   $66.15   $66.15   $66.20  
  Purchase #2 $88.90   12.137%   $99.6898   $99.69   $99.70   $99.70  
  Purchase #3 $167.30   10.611%   $185.0522   $185.05   $185.05   $185.10  
  Purchase #4 $164.97   8.331%   $178.7137   $178.71   $178.70   $178.70  
  Purchase #5 $63.67   11.153%   $70.7711   $70.77   $70.75   $70.80  
  Purchase #6 $61.68   5.363%   $64.9879   $64.99   $65.00   $65.00  
  Purchase #7 $132.74   10.455%   $146.618   $146.62   $146.60   $146.60  
  7 purchase totals = $737.75       $811.9872   $811.98   $811.95   $812.10