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	$10.40	3.793%	$10.7945	$10.79	$10.80	$10.80
Purchase #2	$87.99	4.202%	$91.6873	$91.69	$91.70	$91.70
Purchase #3	$85.32	8.335%	$92.4314	$92.43	$92.45	$92.40
Purchase #4	$84.89	6.742%	$90.6133	$90.61	$90.60	$90.60
Purchase #5	$218.80	10.687%	$242.1832	$242.18	$242.20	$242.20
Purchase #6	$108.29	6.661%	$115.5032	$115.50	$115.50	$115.50
Purchase #7	$155.26	10.719%	$171.9023	$171.90	$171.90	$171.90
7 purchase totals =	$750.95		$815.1152	$815.10	$815.15	$815.10