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	$8.90	12.415%	$10.0049	$10.00	$10.00	$10.00
Purchase #2	$45.79	10.314%	$50.5128	$50.51	$50.50	$50.50
Purchase #3	$78.33	5.398%	$82.5583	$82.56	$82.55	$82.60
Purchase #4	$172.49	5.252%	$181.5492	$181.55	$181.55	$181.50
Purchase #5	$11.48	7.714%	$12.3656	$12.37	$12.35	$12.40
Purchase #6	$141.76	8.324%	$153.5601	$153.56	$153.55	$153.60
Purchase #7	$168.99	11.529%	$188.4729	$188.47	$188.45	$188.50
7 purchase totals =	$627.74		$679.0238	$679.02	$678.95	$679.10