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 $237.59   11.324%   $264.4947   $264.49   $264.50   $264.50  
  Purchase #2 $46.71   10.585%   $51.6543   $51.65   $51.65   $51.70  
  Purchase #3 $197.84   5.545%   $208.8102   $208.81   $208.80   $208.80  
  Purchase #4 $248.66   12.550%   $279.8668   $279.87   $279.85   $279.90  
  Purchase #5 $95.97   11.702%   $107.2004   $107.20   $107.20   $107.20  
  Purchase #6 $212.34   3.567%   $219.9142   $219.91   $219.90   $219.90  
  Purchase #7 $46.36   3.455%   $47.9617   $47.96   $47.95   $48.00  
  7 purchase totals = $1,085.47       $1,179.9023   $1,179.89   $1,179.85   $1,180.00