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	$26.72	10.802%	$29.6063	$29.61	$29.60	$29.60
Purchase #2	$32.80	13.168%	$37.1191	$37.12	$37.10	$37.10
Purchase #3	$56.37	13.634%	$64.0555	$64.06	$64.05	$64.10
Purchase #4	$73.48	4.558%	$76.8292	$76.83	$76.85	$76.80
Purchase #5	$187.40	11.347%	$208.6643	$208.66	$208.65	$208.70
Purchase #6	$35.41	5.612%	$37.3972	$37.40	$37.40	$37.40
Purchase #7	$127.56	3.453%	$131.9646	$131.96	$131.95	$132.00
7 purchase totals =	$539.74		$585.6362	$585.64	$585.60	$585.70