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	$89.74	11.670%	$100.2127	$100.21	$100.20	$100.20
Purchase #2	$200.33	11.720%	$223.8087	$223.81	$223.80	$223.80
Purchase #3	$14.94	8.167%	$16.1601	$16.16	$16.15	$16.20
Purchase #4	$28.40	5.186%	$29.8728	$29.87	$29.85	$29.90
Purchase #5	$117.75	8.594%	$127.8694	$127.87	$127.85	$127.90
Purchase #6	$53.84	9.847%	$59.1416	$59.14	$59.15	$59.10
Purchase #7	$43.29	4.375%	$45.1839	$45.18	$45.20	$45.20
7 purchase totals =	$548.29		$602.2492	$602.24	$602.20	$602.30