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	$70.78	5.173%	$74.4414	$74.44	$74.45	$74.40
Purchase #2	$61.44	7.729%	$66.1887	$66.19	$66.20	$66.20
Purchase #3	$79.32	11.777%	$88.6615	$88.66	$88.65	$88.70
Purchase #4	$50.39	8.811%	$54.8299	$54.83	$54.85	$54.80
Purchase #5	$137.55	4.188%	$143.3106	$143.31	$143.30	$143.30
Purchase #6	$172.54	7.409%	$185.3235	$185.32	$185.30	$185.30
Purchase #7	$18.69	8.681%	$20.3125	$20.31	$20.30	$20.30
7 purchase totals =	$590.71		$633.0681	$633.06	$633.05	$633.00