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	$179.58	5.768%	$189.9382	$189.94	$189.95	$189.90
Purchase #2	$140.76	5.358%	$148.3019	$148.30	$148.30	$148.30
Purchase #3	$19.41	10.643%	$21.4758	$21.48	$21.50	$21.50
Purchase #4	$36.27	12.741%	$40.8912	$40.89	$40.90	$40.90
Purchase #5	$66.94	6.669%	$71.4042	$71.40	$71.40	$71.40
Purchase #6	$14.93	6.692%	$15.9291	$15.93	$15.95	$15.90
Purchase #7	$33.51	3.755%	$34.7683	$34.77	$34.75	$34.80
7 purchase totals =	$491.40		$522.7087	$522.71	$522.75	$522.70