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	$223.51	11.717%	$249.6987	$249.70	$249.70	$249.70
Purchase #2	$197.43	3.514%	$204.3677	$204.37	$204.35	$204.40
Purchase #3	$181.75	4.690%	$190.2741	$190.27	$190.25	$190.30
Purchase #4	$61.81	13.869%	$70.3824	$70.38	$70.40	$70.40
Purchase #5	$146.91	7.859%	$158.4557	$158.46	$158.45	$158.50
Purchase #6	$36.73	13.242%	$41.5938	$41.59	$41.60	$41.60
Purchase #7	$50.80	8.820%	$55.2806	$55.28	$55.30	$55.30
7 purchase totals =	$898.94		$970.0530	$970.05	$970.05	$970.20