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	$131.42	13.579%	$149.2655	$149.27	$149.25	$149.30
Purchase #2	$167.44	4.610%	$175.159	$175.16	$175.15	$175.20
Purchase #3	$250.51	13.390%	$284.0533	$284.05	$284.05	$284.10
Purchase #4	$43.43	4.340%	$45.3149	$45.31	$45.30	$45.30
Purchase #5	$146.43	5.114%	$153.9184	$153.92	$153.90	$153.90
Purchase #6	$38.43	11.303%	$42.7737	$42.77	$42.75	$42.80
Purchase #7	$123.69	7.663%	$133.1684	$133.17	$133.15	$133.20
7 purchase totals =	$901.35		$983.6532	$983.65	$983.55	$983.80