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 $123.28   9.515%   $135.0101   $135.01   $135.00   $135.00  
  Purchase #2 $23.84   3.524%   $24.6801   $24.68   $24.70   $24.70  
  Purchase #3 $126.73   11.221%   $140.9504   $140.95   $140.95   $141.00  
  Purchase #4 $63.26   4.631%   $66.1896   $66.19   $66.20   $66.20  
  Purchase #5 $14.66   10.694%   $16.2277   $16.23   $16.25   $16.20  
  Purchase #6 $200.61   8.296%   $217.2526   $217.25   $217.25   $217.30  
  Purchase #7 $22.97   5.468%   $24.226   $24.23   $24.25   $24.20  
  7 purchase totals = $575.35       $624.5365   $624.54   $624.60   $624.60