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	$11.94	13.874%	$13.5966	$13.60	$13.60	$13.60
Purchase #2	$76.62	11.733%	$85.6098	$85.61	$85.60	$85.60
Purchase #3	$53.74	8.803%	$58.4707	$58.47	$58.45	$58.50
Purchase #4	$170.67	7.525%	$183.5129	$183.51	$183.50	$183.50
Purchase #5	$65.34	12.709%	$73.6441	$73.64	$73.65	$73.60
Purchase #6	$117.74	8.519%	$127.7703	$127.77	$127.75	$127.80
Purchase #7	$17.37	6.349%	$18.4728	$18.47	$18.45	$18.50
7 purchase totals =	$513.42		$561.0772	$561.07	$561.00	$561.10