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 $144.45   12.391%   $162.3488   $162.35   $162.35   $162.30  
  Purchase #2 $191.98   7.620%   $206.6089   $206.61   $206.60   $206.60  
  Purchase #3 $33.49   5.180%   $35.2248   $35.22   $35.20   $35.20  
  Purchase #4 $227.95   9.326%   $249.2086   $249.21   $249.20   $249.20  
  Purchase #5 $77.98   8.514%   $84.6192   $84.62   $84.60   $84.60  
  Purchase #6 $161.90   9.283%   $176.9292   $176.93   $176.95   $176.90  
  Purchase #7 $117.93   7.613%   $126.908   $126.91   $126.90   $126.90  
  7 purchase totals = $955.68       $1,041.8475   $1,041.85   $1,041.80   $1,041.70