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 $67.82   12.728%   $76.4521   $76.45   $76.45   $76.50  
  Purchase #2 $69.53   10.618%   $76.9127   $76.91   $76.90   $76.90  
  Purchase #3 $228.38   3.464%   $236.2911   $236.29   $236.30   $236.30  
  Purchase #4 $89.96   4.299%   $93.8274   $93.83   $93.85   $93.80  
  Purchase #5 $167.53   10.238%   $184.6817   $184.68   $184.70   $184.70  
  Purchase #6 $169.81   6.497%   $180.8426   $180.84   $180.85   $180.80  
  Purchase #7 $169.48   9.734%   $185.9772   $185.98   $186.00   $186.00  
  7 purchase totals = $962.51       $1,034.9848   $1,034.98   $1,035.05   $1,035.00