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	$109.58	12.378%	$123.1438	$123.14	$123.15	$123.10
Purchase #2	$57.99	12.599%	$65.2962	$65.30	$65.30	$65.30
Purchase #3	$37.82	11.491%	$42.1659	$42.17	$42.15	$42.20
Purchase #4	$121.26	5.857%	$128.3622	$128.36	$128.35	$128.40
Purchase #5	$34.78	10.521%	$38.4392	$38.44	$38.45	$38.40
Purchase #6	$82.51	3.815%	$85.6578	$85.66	$85.65	$85.70
Purchase #7	$249.88	11.608%	$278.8861	$278.89	$278.90	$278.90
7 purchase totals =	$693.82		$761.9512	$761.96	$761.95	$762.00