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	$113.35	12.461%	$127.4745	$127.47	$127.45	$127.50
Purchase #2	$129.74	9.665%	$142.2794	$142.28	$142.30	$142.30
Purchase #3	$63.75	9.731%	$69.9535	$69.95	$69.95	$70.00
Purchase #4	$111.79	5.762%	$118.2313	$118.23	$118.25	$118.20
Purchase #5	$135.35	3.347%	$139.8802	$139.88	$139.90	$139.90
Purchase #6	$143.41	12.444%	$161.2559	$161.26	$161.25	$161.30
Purchase #7	$37.54	7.486%	$40.3502	$40.35	$40.35	$40.40
7 purchase totals =	$734.93		$799.4250	$799.42	$799.45	$799.60