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	$246.51	8.798%	$268.1979	$268.20	$268.20	$268.20
Purchase #2	$31.31	13.199%	$35.4426	$35.44	$35.45	$35.40
Purchase #3	$139.48	8.680%	$151.5869	$151.59	$151.60	$151.60
Purchase #4	$224.85	4.754%	$235.5394	$235.54	$235.55	$235.50
Purchase #5	$62.86	13.737%	$71.4951	$71.50	$71.50	$71.50
Purchase #6	$20.69	10.677%	$22.8991	$22.90	$22.90	$22.90
Purchase #7	$57.92	13.680%	$65.8435	$65.84	$65.85	$65.80
7 purchase totals =	$783.62		$851.0045	$851.01	$851.05	$850.90