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	$84.44	5.473%	$89.0614	$89.06	$89.05	$89.10
Purchase #2	$152.88	8.187%	$165.3963	$165.40	$165.40	$165.40
Purchase #3	$92.81	13.482%	$105.3226	$105.32	$105.30	$105.30
Purchase #4	$41.81	3.748%	$43.377	$43.38	$43.40	$43.40
Purchase #5	$137.26	8.383%	$148.7665	$148.77	$148.75	$148.80
Purchase #6	$147.68	9.464%	$161.6564	$161.66	$161.65	$161.70
Purchase #7	$148.89	6.554%	$158.6483	$158.65	$158.65	$158.60
7 purchase totals =	$805.77		$872.2285	$872.24	$872.20	$872.30