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	$124.47	10.560%	$137.614	$137.61	$137.60	$137.60
Purchase #2	$170.45	8.547%	$185.0184	$185.02	$185.00	$185.00
Purchase #3	$133.83	8.544%	$145.2644	$145.26	$145.25	$145.30
Purchase #4	$131.94	4.229%	$137.5197	$137.52	$137.50	$137.50
Purchase #5	$59.49	13.569%	$67.5622	$67.56	$67.55	$67.60
Purchase #6	$32.51	5.319%	$34.2392	$34.24	$34.25	$34.20
Purchase #7	$242.36	4.812%	$254.0224	$254.02	$254.00	$254.00
7 purchase totals =	$895.05		$961.2403	$961.23	$961.15	$961.20