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	$38.28	3.184%	$39.4988	$39.50	$39.50	$39.50
Purchase #2	$139.64	10.209%	$153.8958	$153.90	$153.90	$153.90
Purchase #3	$109.26	13.865%	$124.4089	$124.41	$124.40	$124.40
Purchase #4	$104.68	11.463%	$116.6795	$116.68	$116.70	$116.70
Purchase #5	$59.69	4.768%	$62.536	$62.54	$62.55	$62.50
Purchase #6	$43.53	3.813%	$45.1898	$45.19	$45.20	$45.20
Purchase #7	$175.71	7.292%	$188.5228	$188.52	$188.50	$188.50
7 purchase totals =	$670.79		$730.7316	$730.74	$730.75	$730.70