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	$21.55	6.378%	$22.9245	$22.92	$22.90	$22.90
Purchase #2	$185.78	13.126%	$210.1655	$210.17	$210.15	$210.20
Purchase #3	$235.80	3.431%	$243.8903	$243.89	$243.90	$243.90
Purchase #4	$186.39	5.430%	$196.511	$196.51	$196.50	$196.50
Purchase #5	$191.66	13.433%	$217.4057	$217.41	$217.40	$217.40
Purchase #6	$169.38	12.834%	$191.1182	$191.12	$191.10	$191.10
Purchase #7	$173.35	11.434%	$193.1708	$193.17	$193.15	$193.20
7 purchase totals =	$1,163.91		$1,275.1860	$1,275.19	$1,275.10	$1,275.20