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	$12.74	3.568%	$13.1946	$13.19	$13.20	$13.20
Purchase #2	$78.44	5.231%	$82.5432	$82.54	$82.55	$82.50
Purchase #3	$157.61	9.510%	$172.5987	$172.60	$172.60	$172.60
Purchase #4	$17.68	6.158%	$18.7687	$18.77	$18.75	$18.80
Purchase #5	$241.89	3.477%	$250.3005	$250.30	$250.30	$250.30
Purchase #6	$87.39	3.468%	$90.4207	$90.42	$90.40	$90.40
Purchase #7	$155.96	9.267%	$170.4128	$170.41	$170.40	$170.40
7 purchase totals =	$751.71		$798.2392	$798.23	$798.20	$798.20