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	$27.97	6.416%	$29.7646	$29.76	$29.75	$29.80
Purchase #2	$99.69	11.548%	$111.2022	$111.20	$111.20	$111.20
Purchase #3	$89.72	4.588%	$93.8364	$93.84	$93.85	$93.80
Purchase #4	$168.80	12.497%	$189.8949	$189.89	$189.90	$189.90
Purchase #5	$250.38	10.468%	$276.5898	$276.59	$276.60	$276.60
Purchase #6	$116.96	9.207%	$127.7285	$127.73	$127.75	$127.70
Purchase #7	$158.42	5.799%	$167.6068	$167.61	$167.60	$167.60
7 purchase totals =	$911.94		$996.6232	$996.62	$996.65	$996.60