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 $247.76   7.666%   $266.7533   $266.75   $266.75   $266.80  
  Purchase #2 $59.92   10.155%   $66.0049   $66.00   $66.00   $66.00  
  Purchase #3 $84.25   12.489%   $94.772   $94.77   $94.75   $94.80  
  Purchase #4 $225.35   6.636%   $240.3042   $240.30   $240.30   $240.30  
  Purchase #5 $127.69   10.213%   $140.731   $140.73   $140.75   $140.70  
  Purchase #6 $89.66   13.249%   $101.5391   $101.54   $101.55   $101.50  
  Purchase #7 $24.75   13.659%   $28.1306   $28.13   $28.15   $28.10  
  7 purchase totals = $859.38       $938.2351   $938.22   $938.25   $938.20