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	$241.73	5.761%	$255.6561	$255.66	$255.65	$255.70
Purchase #2	$116.48	13.615%	$132.3388	$132.34	$132.35	$132.30
Purchase #3	$96.25	4.515%	$100.5957	$100.60	$100.60	$100.60
Purchase #4	$237.97	4.318%	$248.2455	$248.25	$248.25	$248.20
Purchase #5	$40.51	5.757%	$42.8422	$42.84	$42.85	$42.80
Purchase #6	$87.46	5.546%	$92.3105	$92.31	$92.30	$92.30
Purchase #7	$144.66	3.237%	$149.3426	$149.34	$149.35	$149.30
7 purchase totals =	$965.06		$1,021.3314	$1,021.34	$1,021.35	$1,021.20