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	$54.37	10.203%	$59.9174	$59.92	$59.90	$59.90
Purchase #2	$30.36	6.788%	$32.4208	$32.42	$32.40	$32.40
Purchase #3	$242.61	13.661%	$275.753	$275.75	$275.75	$275.80
Purchase #4	$69.75	13.845%	$79.4069	$79.41	$79.40	$79.40
Purchase #5	$108.33	5.569%	$114.3629	$114.36	$114.35	$114.40
Purchase #6	$10.33	13.463%	$11.7207	$11.72	$11.70	$11.70
Purchase #7	$94.31	5.296%	$99.3047	$99.30	$99.30	$99.30
7 purchase totals =	$610.06		$672.8864	$672.88	$672.80	$672.90