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 $114.38   8.626%   $124.2464   $124.25   $124.25   $124.20  
  Purchase #2 $54.66   5.578%   $57.7089   $57.71   $57.70   $57.70  
  Purchase #3 $38.59   11.142%   $42.8897   $42.89   $42.90   $42.90  
  Purchase #4 $239.62   4.797%   $251.1146   $251.11   $251.10   $251.10  
  Purchase #5 $71.92   5.309%   $75.7382   $75.74   $75.75   $75.70  
  Purchase #6 $241.99   13.118%   $273.7342   $273.73   $273.75   $273.70  
  Purchase #7 $224.97   3.719%   $233.3366   $233.34   $233.35   $233.30  
  7 purchase totals = $986.13       $1,058.7686   $1,058.77   $1,058.80   $1,058.60