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	$233.28	11.675%	$260.5154	$260.52	$260.50	$260.50
Purchase #2	$195.49	3.642%	$202.6097	$202.61	$202.60	$202.60
Purchase #3	$100.74	11.160%	$111.9826	$111.98	$112.00	$112.00
Purchase #4	$37.79	13.196%	$42.7768	$42.78	$42.80	$42.80
Purchase #5	$136.89	5.335%	$144.1931	$144.19	$144.20	$144.20
Purchase #6	$56.69	13.872%	$64.554	$64.55	$64.55	$64.60
Purchase #7	$19.31	4.586%	$20.1956	$20.20	$20.20	$20.20
7 purchase totals =	$780.19		$846.8272	$846.83	$846.85	$846.90