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 $69.63   8.718%   $75.7003   $75.70   $75.70   $75.70  
  Purchase #2 $157.77   13.283%   $178.7266   $178.73   $178.75   $178.70  
  Purchase #3 $225.95   10.337%   $249.3065   $249.31   $249.30   $249.30  
  Purchase #4 $30.73   9.571%   $33.6712   $33.67   $33.65   $33.70  
  Purchase #5 $103.62   13.787%   $117.9061   $117.91   $117.90   $117.90  
  Purchase #6 $37.95   9.854%   $41.6896   $41.69   $41.70   $41.70  
  Purchase #7 $111.34   6.759%   $118.8655   $118.87   $118.85   $118.90  
  7 purchase totals = $736.99       $815.8658   $815.88   $815.85   $815.90