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	$18.96	10.170%	$20.8882	$20.89	$20.90	$20.90
Purchase #2	$83.97	8.217%	$90.8698	$90.87	$90.85	$90.90
Purchase #3	$11.79	5.746%	$12.4675	$12.47	$12.45	$12.50
Purchase #4	$136.34	12.496%	$153.377	$153.38	$153.40	$153.40
Purchase #5	$146.92	8.113%	$158.8396	$158.84	$158.85	$158.80
Purchase #6	$239.49	13.493%	$271.8044	$271.80	$271.80	$271.80
Purchase #7	$193.81	10.358%	$213.8848	$213.88	$213.90	$213.90
7 purchase totals =	$831.28		$922.1313	$922.13	$922.15	$922.20