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	$246.69	3.442%	$255.1811	$255.18	$255.20	$255.20
Purchase #2	$34.91	10.407%	$38.5431	$38.54	$38.55	$38.50
Purchase #3	$64.72	12.406%	$72.7492	$72.75	$72.75	$72.70
Purchase #4	$227.46	4.667%	$238.0756	$238.08	$238.10	$238.10
Purchase #5	$68.44	12.579%	$77.0491	$77.05	$77.05	$77.00
Purchase #6	$19.50	6.293%	$20.7271	$20.73	$20.75	$20.70
Purchase #7	$41.99	8.455%	$45.5403	$45.54	$45.55	$45.50
7 purchase totals =	$703.71		$747.8655	$747.87	$747.95	$747.70