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	$87.96	13.142%	$99.5197	$99.52	$99.50	$99.50
Purchase #2	$250.36	8.491%	$271.6181	$271.62	$271.60	$271.60
Purchase #3	$129.96	9.826%	$142.7299	$142.73	$142.75	$142.70
Purchase #4	$111.79	13.432%	$126.8056	$126.81	$126.80	$126.80
Purchase #5	$61.80	10.260%	$68.1407	$68.14	$68.15	$68.10
Purchase #6	$28.32	13.874%	$32.2491	$32.25	$32.25	$32.20
Purchase #7	$46.90	11.539%	$52.3118	$52.31	$52.30	$52.30
7 purchase totals =	$717.09		$793.3749	$793.38	$793.35	$793.20