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	$17.73	4.367%	$18.5043	$18.50	$18.50	$18.50
Purchase #2	$102.32	10.111%	$112.6656	$112.67	$112.65	$112.70
Purchase #3	$187.27	9.858%	$205.7311	$205.73	$205.75	$205.70
Purchase #4	$140.67	11.210%	$156.4391	$156.44	$156.45	$156.40
Purchase #5	$135.61	3.582%	$140.4676	$140.47	$140.45	$140.50
Purchase #6	$188.25	4.127%	$196.0191	$196.02	$196.00	$196.00
Purchase #7	$86.57	4.810%	$90.734	$90.73	$90.75	$90.70
7 purchase totals =	$858.42		$920.5608	$920.56	$920.55	$920.50