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	$99.80	11.657%	$111.4337	$111.43	$111.45	$111.40
Purchase #2	$115.45	9.522%	$126.4431	$126.44	$126.45	$126.40
Purchase #3	$45.88	11.142%	$50.9919	$50.99	$51.00	$51.00
Purchase #4	$24.58	13.173%	$27.8179	$27.82	$27.80	$27.80
Purchase #5	$12.45	3.280%	$12.8584	$12.86	$12.85	$12.90
Purchase #6	$223.65	3.685%	$231.8915	$231.89	$231.90	$231.90
Purchase #7	$47.36	3.612%	$49.0706	$49.07	$49.05	$49.10
7 purchase totals =	$569.17		$610.5071	$610.50	$610.50	$610.50