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	$138.67	5.296%	$146.014	$146.01	$146.00	$146.00
Purchase #2	$32.48	7.185%	$34.8137	$34.81	$34.80	$34.80
Purchase #3	$42.86	5.593%	$45.2572	$45.26	$45.25	$45.30
Purchase #4	$194.97	8.714%	$211.9597	$211.96	$211.95	$212.00
Purchase #5	$193.80	3.648%	$200.8698	$200.87	$200.85	$200.90
Purchase #6	$73.51	9.532%	$80.517	$80.52	$80.50	$80.50
Purchase #7	$77.27	6.539%	$82.3227	$82.32	$82.30	$82.30
7 purchase totals =	$753.56		$801.7541	$801.75	$801.65	$801.80