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	$41.27	12.749%	$46.5315	$46.53	$46.55	$46.50
Purchase #2	$36.47	4.636%	$38.1607	$38.16	$38.15	$38.20
Purchase #3	$18.51	11.478%	$20.6346	$20.63	$20.65	$20.60
Purchase #4	$122.56	7.626%	$131.9064	$131.91	$131.90	$131.90
Purchase #5	$243.70	11.348%	$271.3551	$271.36	$271.35	$271.40
Purchase #6	$17.56	8.582%	$19.067	$19.07	$19.05	$19.10
Purchase #7	$111.87	10.703%	$123.8434	$123.84	$123.85	$123.80
7 purchase totals =	$591.94		$651.4987	$651.50	$651.50	$651.50