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	$238.65	3.631%	$247.3154	$247.32	$247.30	$247.30
Purchase #2	$182.55	7.652%	$196.5187	$196.52	$196.50	$196.50
Purchase #3	$182.82	3.458%	$189.1419	$189.14	$189.15	$189.10
Purchase #4	$10.90	13.473%	$12.3686	$12.37	$12.35	$12.40
Purchase #5	$250.77	9.809%	$275.368	$275.37	$275.35	$275.40
Purchase #6	$138.76	10.832%	$153.7905	$153.79	$153.80	$153.80
Purchase #7	$151.53	3.865%	$157.3866	$157.39	$157.40	$157.40
7 purchase totals =	$1,155.98		$1,231.8897	$1,231.90	$1,231.85	$1,231.90