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	$120.76	5.297%	$127.1567	$127.16	$127.15	$127.20
Purchase #2	$137.69	3.739%	$142.8382	$142.84	$142.85	$142.80
Purchase #3	$232.64	6.530%	$247.8314	$247.83	$247.85	$247.80
Purchase #4	$118.28	10.294%	$130.4557	$130.46	$130.45	$130.50
Purchase #5	$93.40	12.516%	$105.0899	$105.09	$105.10	$105.10
Purchase #6	$9.91	12.454%	$11.1442	$11.14	$11.15	$11.10
Purchase #7	$143.88	13.219%	$162.8995	$162.90	$162.90	$162.90
7 purchase totals =	$856.56		$927.4156	$927.42	$927.45	$927.40