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	$96.38	13.132%	$109.0366	$109.04	$109.05	$109.00
Purchase #2	$20.34	5.604%	$21.4799	$21.48	$21.50	$21.50
Purchase #3	$116.75	6.626%	$124.4859	$124.49	$124.50	$124.50
Purchase #4	$130.46	8.296%	$141.283	$141.28	$141.30	$141.30
Purchase #5	$233.91	4.151%	$243.6196	$243.62	$243.60	$243.60
Purchase #6	$127.88	8.707%	$139.0145	$139.01	$139.00	$139.00
Purchase #7	$18.50	10.539%	$20.4497	$20.45	$20.45	$20.40
7 purchase totals =	$744.22		$799.3692	$799.37	$799.40	$799.30