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 $243.59   13.512%   $276.5039   $276.50   $276.50   $276.50  
  Purchase #2 $166.47   4.482%   $173.9312   $173.93   $173.95   $173.90  
  Purchase #3 $145.28   13.145%   $164.3771   $164.38   $164.40   $164.40  
  Purchase #4 $57.66   12.434%   $64.8294   $64.83   $64.85   $64.80  
  Purchase #5 $33.76   11.863%   $37.7649   $37.76   $37.75   $37.80  
  Purchase #6 $214.71   9.660%   $235.451   $235.45   $235.45   $235.50  
  Purchase #7 $8.68   5.124%   $9.1248   $9.12   $9.10   $9.10  
  7 purchase totals = $870.15       $961.9823   $961.97   $962.00   $962.00