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	$18.74	8.722%	$20.3745	$20.37	$20.35	$20.40
Purchase #2	$118.25	8.219%	$127.969	$127.97	$127.95	$128.00
Purchase #3	$59.67	4.255%	$62.209	$62.21	$62.20	$62.20
Purchase #4	$83.83	9.191%	$91.5348	$91.53	$91.55	$91.50
Purchase #5	$72.25	6.104%	$76.6601	$76.66	$76.65	$76.70
Purchase #6	$181.29	6.145%	$192.4303	$192.43	$192.45	$192.40
Purchase #7	$52.35	7.619%	$56.3385	$56.34	$56.35	$56.30
7 purchase totals =	$586.38		$627.5162	$627.51	$627.50	$627.50