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 $51.82   10.590%   $57.3077   $57.31   $57.30   $57.30  
  Purchase #2 $194.95   10.206%   $214.8466   $214.85   $214.85   $214.80  
  Purchase #3 $110.74   13.223%   $125.3832   $125.38   $125.40   $125.40  
  Purchase #4 $194.77   6.513%   $207.4554   $207.46   $207.45   $207.50  
  Purchase #5 $176.37   10.497%   $194.8836   $194.88   $194.90   $194.90  
  Purchase #6 $169.27   11.252%   $188.3163   $188.32   $188.30   $188.30  
  Purchase #7 $45.83   4.712%   $47.9895   $47.99   $48.00   $48.00  
  7 purchase totals = $943.75       $1,036.1823   $1,036.19   $1,036.20   $1,036.20