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 $164.45   11.608%   $183.5394   $183.54   $183.55   $183.50  
  Purchase #2 $157.90   6.290%   $167.8319   $167.83   $167.85   $167.80  
  Purchase #3 $208.71   5.374%   $219.9261   $219.93   $219.95   $219.90  
  Purchase #4 $46.63   7.116%   $49.9482   $49.95   $49.95   $49.90  
  Purchase #5 $21.37   6.540%   $22.7676   $22.77   $22.75   $22.80  
  Purchase #6 $47.67   10.810%   $52.8231   $52.82   $52.80   $52.80  
  Purchase #7 $68.33   3.355%   $70.6225   $70.62   $70.60   $70.60  
  7 purchase totals = $715.06       $767.4588   $767.46   $767.45   $767.30