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	$249.53	10.157%	$274.8748	$274.87	$274.85	$274.90
Purchase #2	$32.88	13.664%	$37.3727	$37.37	$37.35	$37.40
Purchase #3	$69.59	11.498%	$77.5915	$77.59	$77.60	$77.60
Purchase #4	$148.74	12.463%	$167.2775	$167.28	$167.30	$167.30
Purchase #5	$222.29	11.513%	$247.8822	$247.88	$247.90	$247.90
Purchase #6	$46.83	7.858%	$50.5099	$50.51	$50.50	$50.50
Purchase #7	$31.77	7.223%	$34.0647	$34.06	$34.05	$34.10
7 purchase totals =	$801.63		$889.5733	$889.56	$889.55	$889.70