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	$85.36	4.526%	$89.2234	$89.22	$89.20	$89.20
Purchase #2	$211.96	4.691%	$221.903	$221.90	$221.90	$221.90
Purchase #3	$122.39	6.675%	$130.5595	$130.56	$130.55	$130.60
Purchase #4	$131.88	4.772%	$138.1733	$138.17	$138.15	$138.20
Purchase #5	$214.74	12.580%	$241.7543	$241.75	$241.75	$241.80
Purchase #6	$229.40	6.699%	$244.7675	$244.77	$244.75	$244.80
Purchase #7	$20.58	4.568%	$21.5201	$21.52	$21.50	$21.50
7 purchase totals =	$1,016.31		$1,087.9011	$1,087.89	$1,087.80	$1,088.00