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	$81.92	9.471%	$89.6786	$89.68	$89.70	$89.70
Purchase #2	$20.32	9.350%	$22.2199	$22.22	$22.20	$22.20
Purchase #3	$172.96	7.400%	$185.759	$185.76	$185.75	$185.80
Purchase #4	$133.27	8.366%	$144.4194	$144.42	$144.40	$144.40
Purchase #5	$143.92	5.668%	$152.0774	$152.08	$152.10	$152.10
Purchase #6	$87.89	11.196%	$97.7302	$97.73	$97.75	$97.70
Purchase #7	$142.52	9.169%	$155.5877	$155.59	$155.60	$155.60
7 purchase totals =	$782.80		$847.4722	$847.48	$847.50	$847.50