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	$75.77	10.206%	$83.5031	$83.50	$83.50	$83.50
Purchase #2	$172.40	6.506%	$183.6163	$183.62	$183.60	$183.60
Purchase #3	$241.28	3.834%	$250.5307	$250.53	$250.55	$250.50
Purchase #4	$34.85	6.313%	$37.0501	$37.05	$37.05	$37.10
Purchase #5	$195.52	5.377%	$206.0331	$206.03	$206.05	$206.00
Purchase #6	$183.84	4.749%	$192.5706	$192.57	$192.55	$192.60
Purchase #7	$113.75	11.667%	$127.0212	$127.02	$127.00	$127.00
7 purchase totals =	$1,017.41		$1,080.3251	$1,080.32	$1,080.30	$1,080.30