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 $184.85   13.474%   $209.7567   $209.76   $209.75   $209.80  
  Purchase #2 $234.97   4.430%   $245.3792   $245.38   $245.40   $245.40  
  Purchase #3 $236.78   13.839%   $269.548   $269.55   $269.55   $269.50  
  Purchase #4 $217.34   5.774%   $229.8892   $229.89   $229.90   $229.90  
  Purchase #5 $167.61   9.207%   $183.0419   $183.04   $183.05   $183.00  
  Purchase #6 $72.45   9.736%   $79.5037   $79.50   $79.50   $79.50  
  Purchase #7 $215.48   9.682%   $236.3428   $236.34   $236.35   $236.30  
  7 purchase totals = $1,329.48       $1,453.4615   $1,453.46   $1,453.50   $1,453.40