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	$96.89	3.845%	$100.6154	$100.62	$100.60	$100.60
Purchase #2	$103.32	3.659%	$107.1005	$107.10	$107.10	$107.10
Purchase #3	$150.95	6.632%	$160.961	$160.96	$160.95	$161.00
Purchase #4	$154.54	11.624%	$172.5037	$172.50	$172.50	$172.50
Purchase #5	$70.47	13.616%	$80.0652	$80.07	$80.05	$80.10
Purchase #6	$42.65	7.615%	$45.8978	$45.90	$45.90	$45.90
Purchase #7	$164.49	11.454%	$183.3307	$183.33	$183.35	$183.30
7 purchase totals =	$783.31		$850.4743	$850.48	$850.45	$850.50