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	$50.89	7.166%	$54.5368	$54.54	$54.55	$54.50
Purchase #2	$49.29	4.479%	$51.4977	$51.50	$51.50	$51.50
Purchase #3	$95.79	3.648%	$99.2844	$99.28	$99.30	$99.30
Purchase #4	$44.82	13.698%	$50.9594	$50.96	$50.95	$51.00
Purchase #5	$150.82	11.229%	$167.7556	$167.76	$167.75	$167.80
Purchase #6	$56.44	5.303%	$59.433	$59.43	$59.45	$59.40
Purchase #7	$167.77	8.707%	$182.3777	$182.38	$182.40	$182.40
7 purchase totals =	$615.82		$665.8446	$665.85	$665.90	$665.90