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	$222.27	12.752%	$250.6139	$250.61	$250.60	$250.60
Purchase #2	$137.63	4.722%	$144.1289	$144.13	$144.15	$144.10
Purchase #3	$146.64	3.593%	$151.9088	$151.91	$151.90	$151.90
Purchase #4	$202.99	12.568%	$228.5018	$228.50	$228.50	$228.50
Purchase #5	$164.47	9.342%	$179.8348	$179.83	$179.85	$179.80
Purchase #6	$153.94	10.512%	$170.1222	$170.12	$170.10	$170.10
Purchase #7	$176.48	4.109%	$183.7316	$183.73	$183.75	$183.70
7 purchase totals =	$1,204.42		$1,308.8420	$1,308.83	$1,308.85	$1,308.70