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	$19.34	5.722%	$20.4466	$20.45	$20.45	$20.40
Purchase #2	$22.67	11.513%	$25.28	$25.28	$25.30	$25.30
Purchase #3	$94.25	5.816%	$99.7316	$99.73	$99.75	$99.70
Purchase #4	$101.73	4.138%	$105.9396	$105.94	$105.95	$105.90
Purchase #5	$241.60	3.127%	$249.1548	$249.15	$249.15	$249.20
Purchase #6	$34.71	12.535%	$39.0609	$39.06	$39.05	$39.10
Purchase #7	$44.34	9.536%	$48.5683	$48.57	$48.55	$48.60
7 purchase totals =	$558.64		$588.1818	$588.18	$588.20	$588.20