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 $29.36   10.258%   $32.3717   $32.37   $32.35   $32.40  
  Purchase #2 $71.95   13.381%   $81.5776   $81.58   $81.60   $81.60  
  Purchase #3 $240.56   9.672%   $263.827   $263.83   $263.85   $263.80  
  Purchase #4 $154.38   6.826%   $164.918   $164.92   $164.90   $164.90  
  Purchase #5 $195.37   5.303%   $205.7305   $205.73   $205.75   $205.70  
  Purchase #6 $69.98   9.609%   $76.7044   $76.70   $76.70   $76.70  
  Purchase #7 $177.60   11.252%   $197.5836   $197.58   $197.60   $197.60  
  7 purchase totals = $939.20       $1,022.7128   $1,022.71   $1,022.75   $1,022.70