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 $90.79   5.477%   $95.7626   $95.76   $95.75   $95.80  
  Purchase #2 $82.54   12.802%   $93.1068   $93.11   $93.10   $93.10  
  Purchase #3 $139.82   8.269%   $151.3817   $151.38   $151.40   $151.40  
  Purchase #4 $210.97   4.583%   $220.6388   $220.64   $220.65   $220.60  
  Purchase #5 $21.43   10.297%   $23.6366   $23.64   $23.65   $23.60  
  Purchase #6 $86.74   5.860%   $91.823   $91.82   $91.80   $91.80  
  Purchase #7 $84.95   5.792%   $89.8703   $89.87   $89.85   $89.90  
  7 purchase totals = $717.24       $766.2198   $766.22   $766.20   $766.20