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	$94.72	5.548%	$99.9751	$99.98	$100.00	$100.00
Purchase #2	$188.44	4.249%	$196.4468	$196.45	$196.45	$196.40
Purchase #3	$69.52	3.750%	$72.127	$72.13	$72.15	$72.10
Purchase #4	$109.70	9.509%	$120.1314	$120.13	$120.15	$120.10
Purchase #5	$248.50	6.303%	$264.163	$264.16	$264.15	$264.20
Purchase #6	$37.97	9.103%	$41.4264	$41.43	$41.45	$41.40
Purchase #7	$169.68	12.142%	$190.2825	$190.28	$190.30	$190.30
7 purchase totals =	$918.53		$984.5522	$984.56	$984.65	$984.50