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	$8.96	3.678%	$9.2895	$9.29	$9.30	$9.30
Purchase #2	$88.33	12.594%	$99.4543	$99.45	$99.45	$99.50
Purchase #3	$44.35	13.142%	$50.1785	$50.18	$50.20	$50.20
Purchase #4	$158.34	6.416%	$168.4991	$168.50	$168.50	$168.50
Purchase #5	$108.29	7.821%	$116.7594	$116.76	$116.75	$116.80
Purchase #6	$118.50	4.829%	$124.2224	$124.22	$124.20	$124.20
Purchase #7	$156.31	10.305%	$172.4177	$172.42	$172.40	$172.40
7 purchase totals =	$683.08		$740.8209	$740.82	$740.80	$740.90