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	$159.89	3.713%	$165.8267	$165.83	$165.85	$165.80
Purchase #2	$99.38	7.290%	$106.6248	$106.62	$106.60	$106.60
Purchase #3	$90.31	12.130%	$101.2646	$101.26	$101.25	$101.30
Purchase #4	$30.74	3.649%	$31.8617	$31.86	$31.85	$31.90
Purchase #5	$29.90	7.348%	$32.0971	$32.10	$32.10	$32.10
Purchase #6	$133.83	3.731%	$138.8232	$138.82	$138.80	$138.80
Purchase #7	$186.28	13.422%	$211.2825	$211.28	$211.30	$211.30
7 purchase totals =	$730.33		$787.7806	$787.77	$787.75	$787.80