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 $62.95   5.748%   $66.5684   $66.57   $66.55   $66.60  
  Purchase #2 $130.97   12.420%   $147.2365   $147.24   $147.25   $147.20  
  Purchase #3 $126.68   12.593%   $142.6328   $142.63   $142.65   $142.60  
  Purchase #4 $176.34   9.436%   $192.9794   $192.98   $193.00   $193.00  
  Purchase #5 $170.98   13.844%   $194.6505   $194.65   $194.65   $194.70  
  Purchase #6 $62.93   3.387%   $65.0614   $65.06   $65.05   $65.10  
  Purchase #7 $155.38   11.448%   $173.1679   $173.17   $173.15   $173.20  
  7 purchase totals = $886.23       $982.2969   $982.30   $982.30   $982.40