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 $245.67   6.552%   $261.7663   $261.77   $261.75   $261.80  
  Purchase #2 $99.87   8.412%   $108.2711   $108.27   $108.25   $108.30  
  Purchase #3 $248.68   11.388%   $276.9997   $277.00   $277.00   $277.00  
  Purchase #4 $14.93   8.191%   $16.1529   $16.15   $16.15   $16.20  
  Purchase #5 $167.91   12.824%   $189.4428   $189.44   $189.45   $189.40  
  Purchase #6 $236.80   13.859%   $269.6181   $269.62   $269.60   $269.60  
  Purchase #7 $49.40   8.665%   $53.6805   $53.68   $53.70   $53.70  
  7 purchase totals = $1,063.26       $1,175.9314   $1,175.93   $1,175.90   $1,176.00