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	$49.46	13.761%	$56.2662	$56.27	$56.25	$56.30
Purchase #2	$40.30	10.765%	$44.6383	$44.64	$44.65	$44.60
Purchase #3	$18.64	12.281%	$20.9292	$20.93	$20.95	$20.90
Purchase #4	$159.93	9.690%	$175.4272	$175.43	$175.45	$175.40
Purchase #5	$29.88	5.567%	$31.5434	$31.54	$31.55	$31.50
Purchase #6	$30.72	13.615%	$34.9025	$34.90	$34.90	$34.90
Purchase #7	$118.69	7.767%	$127.9087	$127.91	$127.90	$127.90
7 purchase totals =	$447.62		$491.6155	$491.62	$491.65	$491.50