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 $66.91   9.611%   $73.3407   $73.34   $73.35   $73.30  
  Purchase #2 $249.46   7.413%   $267.9525   $267.95   $267.95   $268.00  
  Purchase #3 $105.85   7.324%   $113.6025   $113.60   $113.60   $113.60  
  Purchase #4 $179.95   11.223%   $200.1458   $200.15   $200.15   $200.10  
  Purchase #5 $15.58   11.862%   $17.4281   $17.43   $17.45   $17.40  
  Purchase #6 $90.38   6.706%   $96.4409   $96.44   $96.45   $96.40  
  Purchase #7 $16.80   5.808%   $17.7757   $17.78   $17.80   $17.80  
  7 purchase totals = $724.93       $786.6862   $786.69   $786.75   $786.60