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	$9.63	7.391%	$10.3418	$10.34	$10.35	$10.30
Purchase #2	$42.52	12.643%	$47.8958	$47.90	$47.90	$47.90
Purchase #3	$46.62	11.159%	$51.8223	$51.82	$51.80	$51.80
Purchase #4	$18.81	7.132%	$20.1515	$20.15	$20.15	$20.20
Purchase #5	$53.31	13.752%	$60.6412	$60.64	$60.65	$60.60
Purchase #6	$38.62	7.364%	$41.464	$41.46	$41.45	$41.50
Purchase #7	$122.51	4.310%	$127.7902	$127.79	$127.80	$127.80
7 purchase totals =	$332.02		$360.1068	$360.10	$360.10	$360.10