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 $36.61   11.117%   $40.6799   $40.68   $40.70   $40.70  
  Purchase #2 $60.38   11.708%   $67.4493   $67.45   $67.45   $67.40  
  Purchase #3 $119.95   4.405%   $125.2338   $125.23   $125.25   $125.20  
  Purchase #4 $72.30   5.812%   $76.5021   $76.50   $76.50   $76.50  
  Purchase #5 $62.53   9.159%   $68.2571   $68.26   $68.25   $68.30  
  Purchase #6 $119.98   12.551%   $135.0387   $135.04   $135.05   $135.00  
  Purchase #7 $174.37   11.104%   $193.732   $193.73   $193.75   $193.70  
  7 purchase totals = $646.12       $706.8929   $706.89   $706.95   $706.80