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	$76.93	10.376%	$84.9123	$84.91	$84.90	$84.90
Purchase #2	$31.29	6.748%	$33.4014	$33.40	$33.40	$33.40
Purchase #3	$151.49	5.161%	$159.3084	$159.31	$159.30	$159.30
Purchase #4	$215.97	12.641%	$243.2708	$243.27	$243.25	$243.30
Purchase #5	$143.89	11.274%	$160.1122	$160.11	$160.10	$160.10
Purchase #6	$140.43	8.120%	$151.8329	$151.83	$151.85	$151.80
Purchase #7	$123.46	3.426%	$127.6897	$127.69	$127.70	$127.70
7 purchase totals =	$883.46		$960.5277	$960.52	$960.50	$960.50