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 $182.91   13.472%   $207.5516   $207.55   $207.55   $207.60  
  Purchase #2 $240.63   4.581%   $251.6533   $251.65   $251.65   $251.70  
  Purchase #3 $42.87   12.703%   $48.3158   $48.32   $48.30   $48.30  
  Purchase #4 $206.26   5.666%   $217.9467   $217.95   $217.95   $217.90  
  Purchase #5 $190.98   9.246%   $208.638   $208.64   $208.65   $208.60  
  Purchase #6 $63.54   13.170%   $71.9082   $71.91   $71.90   $71.90  
  Purchase #7 $75.49   9.179%   $82.4192   $82.42   $82.40   $82.40  
  7 purchase totals = $1,002.68       $1,088.4328   $1,088.44   $1,088.40   $1,088.40