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 $59.84   4.250%   $62.3832   $62.38   $62.40   $62.40  
  Purchase #2 $163.61   8.687%   $177.8228   $177.82   $177.80   $177.80  
  Purchase #3 $130.82   9.132%   $142.7665   $142.77   $142.75   $142.80  
  Purchase #4 $176.99   3.292%   $182.8165   $182.82   $182.80   $182.80  
  Purchase #5 $92.73   11.746%   $103.6221   $103.62   $103.60   $103.60  
  Purchase #6 $79.95   5.277%   $84.169   $84.17   $84.15   $84.20  
  Purchase #7 $42.81   4.669%   $44.8088   $44.81   $44.80   $44.80  
  7 purchase totals = $746.75       $798.3889   $798.39   $798.30   $798.40