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	$223.51	12.296%	$250.9928	$250.99	$251.00	$251.00
Purchase #2	$88.50	4.473%	$92.4586	$92.46	$92.45	$92.50
Purchase #3	$222.35	7.103%	$238.1435	$238.14	$238.15	$238.10
Purchase #4	$211.86	11.673%	$236.5904	$236.59	$236.60	$236.60
Purchase #5	$80.78	11.122%	$89.7644	$89.76	$89.75	$89.80
Purchase #6	$230.27	5.140%	$242.1059	$242.11	$242.10	$242.10
Purchase #7	$40.33	13.770%	$45.8834	$45.88	$45.90	$45.90
7 purchase totals =	$1,097.60		$1,195.9390	$1,195.93	$1,195.95	$1,196.00