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	$18.50	6.187%	$19.6446	$19.64	$19.65	$19.60
Purchase #2	$30.65	9.446%	$33.5452	$33.55	$33.55	$33.50
Purchase #3	$207.37	4.592%	$216.8924	$216.89	$216.90	$216.90
Purchase #4	$100.96	10.538%	$111.5992	$111.60	$111.60	$111.60
Purchase #5	$204.41	11.680%	$228.2851	$228.29	$228.30	$228.30
Purchase #6	$87.63	10.400%	$96.7435	$96.74	$96.75	$96.70
Purchase #7	$97.58	9.238%	$106.5944	$106.59	$106.60	$106.60
7 purchase totals =	$747.10		$813.3044	$813.30	$813.35	$813.20