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	$123.50	8.799%	$134.3668	$134.37	$134.35	$134.40
Purchase #2	$209.76	13.718%	$238.5349	$238.53	$238.55	$238.50
Purchase #3	$159.87	8.381%	$173.2687	$173.27	$173.25	$173.30
Purchase #4	$61.56	11.786%	$68.8155	$68.82	$68.80	$68.80
Purchase #5	$241.69	12.127%	$270.9997	$271.00	$271.00	$271.00
Purchase #6	$151.30	4.591%	$158.2462	$158.25	$158.25	$158.20
Purchase #7	$43.49	4.625%	$45.5014	$45.50	$45.50	$45.50
7 purchase totals =	$991.17		$1,089.7332	$1,089.74	$1,089.70	$1,089.70