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	$17.62	3.473%	$18.2319	$18.23	$18.25	$18.20
Purchase #2	$159.82	13.193%	$180.9051	$180.91	$180.90	$180.90
Purchase #3	$103.84	7.181%	$111.2968	$111.30	$111.30	$111.30
Purchase #4	$106.39	11.735%	$118.8749	$118.87	$118.85	$118.90
Purchase #5	$162.94	5.828%	$172.4361	$172.44	$172.45	$172.40
Purchase #6	$62.89	11.793%	$70.3066	$70.31	$70.30	$70.30
Purchase #7	$197.65	7.394%	$212.2642	$212.26	$212.25	$212.30
7 purchase totals =	$811.15		$884.3156	$884.32	$884.30	$884.30