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	$129.96	3.264%	$134.2019	$134.20	$134.20	$134.20
Purchase #2	$29.91	4.603%	$31.2868	$31.29	$31.30	$31.30
Purchase #3	$54.76	11.812%	$61.2283	$61.23	$61.25	$61.20
Purchase #4	$50.95	8.520%	$55.2909	$55.29	$55.30	$55.30
Purchase #5	$99.37	9.414%	$108.7247	$108.72	$108.70	$108.70
Purchase #6	$46.72	13.407%	$52.9838	$52.98	$53.00	$53.00
Purchase #7	$172.92	13.509%	$196.2798	$196.28	$196.30	$196.30
7 purchase totals =	$584.59		$639.9962	$639.99	$640.05	$640.00