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	$122.49	3.106%	$126.2945	$126.29	$126.30	$126.30
Purchase #2	$195.85	7.323%	$210.1921	$210.19	$210.20	$210.20
Purchase #3	$78.66	8.140%	$85.0629	$85.06	$85.05	$85.10
Purchase #4	$141.29	13.792%	$160.7767	$160.78	$160.80	$160.80
Purchase #5	$177.92	4.276%	$185.5279	$185.53	$185.55	$185.50
Purchase #6	$74.92	4.157%	$78.0344	$78.03	$78.05	$78.00
Purchase #7	$40.51	13.177%	$45.848	$45.85	$45.85	$45.80
7 purchase totals =	$831.64		$891.7365	$891.73	$891.80	$891.70