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	$114.49	12.659%	$128.9833	$128.98	$129.00	$129.00
Purchase #2	$95.61	8.206%	$103.4558	$103.46	$103.45	$103.50
Purchase #3	$146.48	12.147%	$164.2729	$164.27	$164.25	$164.30
Purchase #4	$103.76	7.196%	$111.2266	$111.23	$111.25	$111.20
Purchase #5	$141.55	3.516%	$146.5269	$146.53	$146.55	$146.50
Purchase #6	$52.65	10.466%	$58.1603	$58.16	$58.15	$58.20
Purchase #7	$15.93	9.777%	$17.4875	$17.49	$17.50	$17.50
7 purchase totals =	$670.47		$730.1133	$730.12	$730.15	$730.20