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 $89.97   7.252%   $96.4946   $96.49   $96.50   $96.50  
  Purchase #2 $243.76   7.732%   $262.6075   $262.61   $262.60   $262.60  
  Purchase #3 $136.37   8.726%   $148.2696   $148.27   $148.25   $148.30  
  Purchase #4 $78.63   11.687%   $87.8195   $87.82   $87.80   $87.80  
  Purchase #5 $135.86   11.833%   $151.9363   $151.94   $151.95   $151.90  
  Purchase #6 $174.39   13.203%   $197.4147   $197.41   $197.40   $197.40  
  Purchase #7 $78.77   4.799%   $82.5502   $82.55   $82.55   $82.60  
  7 purchase totals = $937.75       $1,027.0924   $1,027.09   $1,027.05   $1,027.10