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 $10.94   6.251%   $11.6239   $11.62   $11.60   $11.60  
  Purchase #2 $227.69   10.706%   $252.0665   $252.07   $252.05   $252.10  
  Purchase #3 $129.77   13.725%   $147.5809   $147.58   $147.60   $147.60  
  Purchase #4 $60.92   7.519%   $65.5006   $65.50   $65.50   $65.50  
  Purchase #5 $76.64   10.771%   $84.8949   $84.89   $84.90   $84.90  
  Purchase #6 $164.65   13.750%   $187.2894   $187.29   $187.30   $187.30  
  Purchase #7 $210.73   10.710%   $233.2992   $233.30   $233.30   $233.30  
  7 purchase totals = $881.34       $982.2554   $982.25   $982.25   $982.30