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 $241.93   8.267%   $261.9304   $261.93   $261.95   $261.90  
  Purchase #2 $19.26   10.149%   $21.2147   $21.21   $21.20   $21.20  
  Purchase #3 $15.98   9.831%   $17.551   $17.55   $17.55   $17.60  
  Purchase #4 $170.71   8.227%   $184.7543   $184.75   $184.75   $184.80  
  Purchase #5 $154.50   3.284%   $159.5738   $159.57   $159.55   $159.60  
  Purchase #6 $160.59   13.407%   $182.1203   $182.12   $182.10   $182.10  
  Purchase #7 $45.40   9.662%   $49.7865   $49.79   $49.80   $49.80  
  7 purchase totals = $808.37       $876.9310   $876.92   $876.90   $877.00