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	$244.88	4.769%	$256.5583	$256.56	$256.55	$256.60
Purchase #2	$38.59	8.643%	$41.9253	$41.93	$41.95	$41.90
Purchase #3	$98.64	5.346%	$103.9133	$103.91	$103.90	$103.90
Purchase #4	$33.50	3.383%	$34.6333	$34.63	$34.65	$34.60
Purchase #5	$210.87	9.594%	$231.1009	$231.10	$231.10	$231.10
Purchase #6	$32.59	5.342%	$34.331	$34.33	$34.35	$34.30
Purchase #7	$34.89	9.522%	$38.2122	$38.21	$38.20	$38.20
7 purchase totals =	$693.96		$740.6743	$740.67	$740.70	$740.60