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	$85.88	5.707%	$90.7812	$90.78	$90.80	$90.80
Purchase #2	$151.97	3.639%	$157.5002	$157.50	$157.50	$157.50
Purchase #3	$241.70	11.805%	$270.2327	$270.23	$270.25	$270.20
Purchase #4	$105.30	10.553%	$116.4123	$116.41	$116.40	$116.40
Purchase #5	$171.50	4.674%	$179.5159	$179.52	$179.50	$179.50
Purchase #6	$82.77	11.683%	$92.44	$92.44	$92.45	$92.40
Purchase #7	$64.71	6.811%	$69.1174	$69.12	$69.10	$69.10
7 purchase totals =	$903.83		$975.9997	$976.00	$976.00	$975.90