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 $32.49   11.797%   $36.3228   $36.32   $36.30   $36.30  
  Purchase #2 $16.28   3.869%   $16.9099   $16.91   $16.90   $16.90  
  Purchase #3 $197.71   10.286%   $218.0465   $218.05   $218.05   $218.00  
  Purchase #4 $14.47   13.143%   $16.3718   $16.37   $16.35   $16.40  
  Purchase #5 $84.76   8.771%   $92.1943   $92.19   $92.20   $92.20  
  Purchase #6 $195.42   3.552%   $202.3613   $202.36   $202.35   $202.40  
  Purchase #7 $216.56   7.631%   $233.0857   $233.09   $233.10   $233.10  
  7 purchase totals = $757.69       $815.2923   $815.29   $815.25   $815.30