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	$198.91	3.709%	$206.2876	$206.29	$206.30	$206.30
Purchase #2	$156.98	12.670%	$176.8694	$176.87	$176.85	$176.90
Purchase #3	$85.38	6.374%	$90.8221	$90.82	$90.80	$90.80
Purchase #4	$193.36	13.324%	$219.1233	$219.12	$219.10	$219.10
Purchase #5	$138.29	11.286%	$153.8974	$153.90	$153.90	$153.90
Purchase #6	$223.62	8.113%	$241.7623	$241.76	$241.75	$241.80
Purchase #7	$55.52	12.762%	$62.6055	$62.61	$62.60	$62.60
7 purchase totals =	$1,052.06		$1,151.3676	$1,151.37	$1,151.30	$1,151.40