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	$19.84	7.663%	$21.3603	$21.36	$21.35	$21.40
Purchase #2	$167.76	11.733%	$187.4433	$187.44	$187.45	$187.40
Purchase #3	$179.76	10.546%	$198.7175	$198.72	$198.70	$198.70
Purchase #4	$127.64	11.290%	$142.0506	$142.05	$142.05	$142.10
Purchase #5	$188.27	10.685%	$208.3866	$208.39	$208.40	$208.40
Purchase #6	$17.49	6.572%	$18.6394	$18.64	$18.65	$18.60
Purchase #7	$175.28	6.818%	$187.2306	$187.23	$187.25	$187.20
7 purchase totals =	$876.04		$963.8283	$963.83	$963.85	$963.80