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 $115.74   3.534%   $119.8303   $119.83   $119.85   $119.80  
  Purchase #2 $20.87   9.775%   $22.91   $22.91   $22.90   $22.90  
  Purchase #3 $73.84   4.620%   $77.2514   $77.25   $77.25   $77.30  
  Purchase #4 $248.44   8.466%   $269.4729   $269.47   $269.45   $269.50  
  Purchase #5 $45.99   4.414%   $48.02   $48.02   $48.00   $48.00  
  Purchase #6 $157.77   4.217%   $164.4232   $164.42   $164.40   $164.40  
  Purchase #7 $42.65   6.782%   $45.5425   $45.54   $45.55   $45.50  
  7 purchase totals = $705.30       $747.4503   $747.44   $747.40   $747.40