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	$21.40	13.519%	$24.2931	$24.29	$24.30	$24.30
Purchase #2	$45.84	9.314%	$50.1095	$50.11	$50.10	$50.10
Purchase #3	$52.29	4.619%	$54.7053	$54.71	$54.70	$54.70
Purchase #4	$234.60	10.509%	$259.2541	$259.25	$259.25	$259.30
Purchase #5	$33.36	5.140%	$35.0747	$35.07	$35.05	$35.10
Purchase #6	$124.84	4.550%	$130.5202	$130.52	$130.50	$130.50
Purchase #7	$128.32	13.475%	$145.6111	$145.61	$145.60	$145.60
7 purchase totals =	$640.65		$699.5680	$699.56	$699.50	$699.60