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	$162.49	6.408%	$172.9024	$172.90	$172.90	$172.90
Purchase #2	$146.85	4.409%	$153.3246	$153.32	$153.30	$153.30
Purchase #3	$174.98	9.548%	$191.6871	$191.69	$191.70	$191.70
Purchase #4	$10.95	13.851%	$12.4667	$12.47	$12.45	$12.50
Purchase #5	$156.29	8.743%	$169.9544	$169.95	$169.95	$170.00
Purchase #6	$81.85	5.866%	$86.6513	$86.65	$86.65	$86.70
Purchase #7	$181.37	7.104%	$194.2545	$194.25	$194.25	$194.30
7 purchase totals =	$914.78		$981.2410	$981.23	$981.20	$981.40