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 $6.77   12.139%   $7.5918   $7.59   $7.60   $7.60  
  Purchase #2 $209.38   12.194%   $234.9118   $234.91   $234.90   $234.90  
  Purchase #3 $234.68   4.772%   $245.8789   $245.88   $245.90   $245.90  
  Purchase #4 $151.44   5.191%   $159.3013   $159.30   $159.30   $159.30  
  Purchase #5 $239.89   11.199%   $266.7553   $266.76   $266.75   $266.80  
  Purchase #6 $207.45   3.208%   $214.105   $214.11   $214.10   $214.10  
  Purchase #7 $152.81   13.318%   $173.1612   $173.16   $173.15   $173.20  
  7 purchase totals = $1,202.42       $1,301.7053   $1,301.71   $1,301.70   $1,301.80