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	$17.98	9.249%	$19.643	$19.64	$19.65	$19.60
Purchase #2	$111.37	6.396%	$118.4932	$118.49	$118.50	$118.50
Purchase #3	$56.31	5.861%	$59.6103	$59.61	$59.60	$59.60
Purchase #4	$72.79	12.682%	$82.0212	$82.02	$82.00	$82.00
Purchase #5	$85.87	10.251%	$94.6725	$94.67	$94.65	$94.70
Purchase #6	$124.45	7.204%	$133.4154	$133.42	$133.40	$133.40
Purchase #7	$118.74	4.520%	$124.107	$124.11	$124.10	$124.10
7 purchase totals =	$587.51		$631.9626	$631.96	$631.90	$631.90