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	$127.89	9.552%	$140.1061	$140.11	$140.10	$140.10
Purchase #2	$67.33	5.813%	$71.2439	$71.24	$71.25	$71.20
Purchase #3	$192.82	6.213%	$204.7999	$204.80	$204.80	$204.80
Purchase #4	$49.53	10.427%	$54.6945	$54.69	$54.70	$54.70
Purchase #5	$79.42	4.667%	$83.1265	$83.13	$83.15	$83.10
Purchase #6	$235.73	6.169%	$250.2722	$250.27	$250.25	$250.30
Purchase #7	$19.85	6.714%	$21.1827	$21.18	$21.20	$21.20
7 purchase totals =	$772.57		$825.4258	$825.42	$825.45	$825.40