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 $12.33   4.561%   $12.8924   $12.89   $12.90   $12.90  
  Purchase #2 $40.30   4.670%   $42.182   $42.18   $42.20   $42.20  
  Purchase #3 $135.85   3.521%   $140.6333   $140.63   $140.65   $140.60  
  Purchase #4 $102.66   13.189%   $116.1998   $116.20   $116.20   $116.20  
  Purchase #5 $129.41   6.782%   $138.1866   $138.19   $138.20   $138.20  
  Purchase #6 $86.40   6.741%   $92.2242   $92.22   $92.20   $92.20  
  Purchase #7 $142.44   10.156%   $156.9062   $156.91   $156.90   $156.90  
  7 purchase totals = $649.39       $699.2245   $699.22   $699.25   $699.20