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 $238.90   11.854%   $267.2192   $267.22   $267.20   $267.20  
  Purchase #2 $178.37   10.480%   $197.0632   $197.06   $197.05   $197.10  
  Purchase #3 $48.75   5.868%   $51.6107   $51.61   $51.60   $51.60  
  Purchase #4 $143.93   11.832%   $160.9598   $160.96   $160.95   $161.00  
  Purchase #5 $200.56   11.742%   $224.1098   $224.11   $224.10   $224.10  
  Purchase #6 $117.71   8.374%   $127.567   $127.57   $127.55   $127.60  
  Purchase #7 $67.73   10.862%   $75.0868   $75.09   $75.10   $75.10  
  7 purchase totals = $995.95       $1,103.6165   $1,103.62   $1,103.55   $1,103.70