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 $109.80   13.562%   $124.6911   $124.69   $124.70   $124.70  
  Purchase #2 $82.25   11.384%   $91.6133   $91.61   $91.60   $91.60  
  Purchase #3 $93.54   12.463%   $105.1979   $105.20   $105.20   $105.20  
  Purchase #4 $211.88   7.271%   $227.2858   $227.29   $227.30   $227.30  
  Purchase #5 $44.41   7.548%   $47.7621   $47.76   $47.75   $47.80  
  Purchase #6 $205.95   9.283%   $225.0683   $225.07   $225.05   $225.10  
  Purchase #7 $249.43   4.234%   $259.9909   $259.99   $260.00   $260.00  
  7 purchase totals = $997.26       $1,081.6094   $1,081.61   $1,081.60   $1,081.70