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 $240.28   11.662%   $268.3015   $268.30   $268.30   $268.30  
  Purchase #2 $86.82   3.272%   $89.6608   $89.66   $89.65   $89.70  
  Purchase #3 $162.36   10.137%   $178.8184   $178.82   $178.80   $178.80  
  Purchase #4 $44.73   13.234%   $50.6496   $50.65   $50.65   $50.60  
  Purchase #5 $151.30   13.132%   $171.1687   $171.17   $171.15   $171.20  
  Purchase #6 $39.50   3.207%   $40.7668   $40.77   $40.75   $40.80  
  Purchase #7 $69.34   9.233%   $75.7422   $75.74   $75.75   $75.70  
  7 purchase totals = $794.33       $875.1080   $875.11   $875.05   $875.10