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	$123.43	10.874%	$136.8518	$136.85	$136.85	$136.90
Purchase #2	$118.79	11.154%	$132.0398	$132.04	$132.05	$132.00
Purchase #3	$10.65	8.183%	$11.5215	$11.52	$11.50	$11.50
Purchase #4	$87.81	3.701%	$91.0598	$91.06	$91.05	$91.10
Purchase #5	$211.60	5.141%	$222.4784	$222.48	$222.50	$222.50
Purchase #6	$179.30	5.346%	$188.8854	$188.89	$188.90	$188.90
Purchase #7	$204.68	3.218%	$211.2666	$211.27	$211.25	$211.30
7 purchase totals =	$936.26		$994.1033	$994.11	$994.10	$994.20