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	$238.83	13.755%	$271.6811	$271.68	$271.70	$271.70
Purchase #2	$91.61	8.378%	$99.2851	$99.29	$99.30	$99.30
Purchase #3	$95.72	10.377%	$105.6529	$105.65	$105.65	$105.70
Purchase #4	$78.33	6.577%	$83.4818	$83.48	$83.50	$83.50
Purchase #5	$172.45	5.763%	$182.3883	$182.39	$182.40	$182.40
Purchase #6	$127.41	12.580%	$143.4382	$143.44	$143.45	$143.40
Purchase #7	$32.60	3.256%	$33.6615	$33.66	$33.65	$33.70
7 purchase totals =	$836.95		$919.5889	$919.59	$919.65	$919.70