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 $193.97   10.817%   $214.9517   $214.95   $214.95   $215.00  
  Purchase #2 $129.38   10.331%   $142.7462   $142.75   $142.75   $142.70  
  Purchase #3 $230.53   12.379%   $259.0673   $259.07   $259.05   $259.10  
  Purchase #4 $14.77   4.153%   $15.3834   $15.38   $15.40   $15.40  
  Purchase #5 $62.95   5.297%   $66.2845   $66.28   $66.30   $66.30  
  Purchase #6 $56.29   11.129%   $62.5545   $62.55   $62.55   $62.60  
  Purchase #7 $222.64   3.733%   $230.9512   $230.95   $230.95   $231.00  
  7 purchase totals = $910.53       $991.9388   $991.93   $991.95   $992.10