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	$45.41	10.316%	$50.0945	$50.09	$50.10	$50.10
Purchase #2	$86.75	6.436%	$92.3332	$92.33	$92.35	$92.30
Purchase #3	$118.46	7.789%	$127.6868	$127.69	$127.70	$127.70
Purchase #4	$121.55	7.278%	$130.3964	$130.40	$130.40	$130.40
Purchase #5	$9.66	13.298%	$10.9446	$10.94	$10.95	$10.90
Purchase #6	$41.70	4.314%	$43.4989	$43.50	$43.50	$43.50
Purchase #7	$50.53	5.229%	$53.1722	$53.17	$53.15	$53.20
7 purchase totals =	$474.06		$508.1266	$508.12	$508.15	$508.10