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	$173.54	11.358%	$193.2507	$193.25	$193.25	$193.30
Purchase #2	$37.76	9.341%	$41.2872	$41.29	$41.30	$41.30
Purchase #3	$212.61	13.421%	$241.1444	$241.14	$241.15	$241.10
Purchase #4	$195.85	13.718%	$222.7167	$222.72	$222.70	$222.70
Purchase #5	$52.51	11.494%	$58.5455	$58.55	$58.55	$58.50
Purchase #6	$117.88	7.786%	$127.0581	$127.06	$127.05	$127.10
Purchase #7	$40.95	11.754%	$45.7633	$45.76	$45.75	$45.80
7 purchase totals =	$831.10		$929.7659	$929.77	$929.75	$929.80