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	$216.81	12.105%	$243.0549	$243.05	$243.05	$243.10
Purchase #2	$135.69	7.531%	$145.9088	$145.91	$145.90	$145.90
Purchase #3	$104.39	10.648%	$115.5054	$115.51	$115.50	$115.50
Purchase #4	$77.43	6.694%	$82.6132	$82.61	$82.60	$82.60
Purchase #5	$138.40	4.378%	$144.4592	$144.46	$144.45	$144.50
Purchase #6	$161.32	7.222%	$172.9705	$172.97	$172.95	$173.00
Purchase #7	$80.82	3.779%	$83.8742	$83.87	$83.85	$83.90
7 purchase totals =	$914.86		$988.3862	$988.38	$988.30	$988.50