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 $58.94   6.647%   $62.8577   $62.86   $62.85   $62.90  
  Purchase #2 $149.92   12.611%   $168.8264   $168.83   $168.85   $168.80  
  Purchase #3 $127.64   3.616%   $132.2555   $132.26   $132.25   $132.30  
  Purchase #4 $99.31   11.104%   $110.3374   $110.34   $110.35   $110.30  
  Purchase #5 $62.82   9.246%   $68.6283   $68.63   $68.65   $68.60  
  Purchase #6 $226.45   3.256%   $233.8232   $233.82   $233.80   $233.80  
  Purchase #7 $104.61   5.388%   $110.2464   $110.25   $110.25   $110.20  
  7 purchase totals = $829.69       $886.9749   $886.99   $887.00   $886.90