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	$17.84	9.731%	$19.576	$19.58	$19.60	$19.60
Purchase #2	$209.87	7.503%	$225.6165	$225.62	$225.60	$225.60
Purchase #3	$35.71	10.141%	$39.3314	$39.33	$39.35	$39.30
Purchase #4	$236.91	10.638%	$262.1125	$262.11	$262.10	$262.10
Purchase #5	$116.34	8.371%	$126.0788	$126.08	$126.10	$126.10
Purchase #6	$100.56	10.578%	$111.1972	$111.20	$111.20	$111.20
Purchase #7	$113.33	12.427%	$127.4135	$127.41	$127.40	$127.40
7 purchase totals =	$830.56		$911.3259	$911.33	$911.35	$911.30