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	$92.64	8.124%	$100.1661	$100.17	$100.15	$100.20
Purchase #2	$86.41	11.616%	$96.4474	$96.45	$96.45	$96.40
Purchase #3	$45.44	11.647%	$50.7324	$50.73	$50.75	$50.70
Purchase #4	$231.48	4.810%	$242.6142	$242.61	$242.60	$242.60
Purchase #5	$179.53	10.569%	$198.5045	$198.50	$198.50	$198.50
Purchase #6	$61.51	4.391%	$64.2109	$64.21	$64.20	$64.20
Purchase #7	$38.92	13.426%	$44.1454	$44.15	$44.15	$44.10
7 purchase totals =	$735.93		$796.8209	$796.82	$796.80	$796.70