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 $168.69   8.450%   $182.9443   $182.94   $182.95   $182.90  
  Purchase #2 $118.26   7.613%   $127.2631   $127.26   $127.25   $127.30  
  Purchase #3 $237.95   6.803%   $254.1377   $254.14   $254.15   $254.10  
  Purchase #4 $157.28   4.590%   $164.4992   $164.50   $164.50   $164.50  
  Purchase #5 $192.40   4.707%   $201.4563   $201.46   $201.45   $201.50  
  Purchase #6 $159.77   6.491%   $170.1407   $170.14   $170.15   $170.10  
  Purchase #7 $139.69   7.734%   $150.4936   $150.49   $150.50   $150.50  
  7 purchase totals = $1,174.04       $1,250.9349   $1,250.93   $1,250.95   $1,250.90