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	$101.82	10.422%	$112.4317	$112.43	$112.45	$112.40
Purchase #2	$208.59	11.273%	$232.1044	$232.10	$232.10	$232.10
Purchase #3	$134.74	4.304%	$140.5392	$140.54	$140.55	$140.50
Purchase #4	$28.72	3.699%	$29.7824	$29.78	$29.80	$29.80
Purchase #5	$38.78	5.114%	$40.7632	$40.76	$40.75	$40.80
Purchase #6	$157.68	13.363%	$178.7508	$178.75	$178.75	$178.80
Purchase #7	$99.81	12.140%	$111.9269	$111.93	$111.95	$111.90
7 purchase totals =	$770.14		$846.2986	$846.29	$846.35	$846.30