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	$201.97	10.478%	$223.1324	$223.13	$223.15	$223.10
Purchase #2	$64.50	12.234%	$72.3909	$72.39	$72.40	$72.40
Purchase #3	$247.90	12.825%	$279.6932	$279.69	$279.70	$279.70
Purchase #4	$50.51	9.268%	$55.1913	$55.19	$55.20	$55.20
Purchase #5	$10.40	13.628%	$11.8173	$11.82	$11.80	$11.80
Purchase #6	$67.68	5.735%	$71.5614	$71.56	$71.55	$71.60
Purchase #7	$16.66	8.393%	$18.0583	$18.06	$18.05	$18.10
7 purchase totals =	$659.62		$731.8448	$731.84	$731.85	$731.90