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	$84.43	6.332%	$89.7761	$89.78	$89.80	$89.80
Purchase #2	$134.72	12.257%	$151.2326	$151.23	$151.25	$151.20
Purchase #3	$83.85	4.166%	$87.3432	$87.34	$87.35	$87.30
Purchase #4	$113.50	13.208%	$128.4911	$128.49	$128.50	$128.50
Purchase #5	$81.25	13.873%	$92.5218	$92.52	$92.50	$92.50
Purchase #6	$23.89	10.626%	$26.4286	$26.43	$26.45	$26.40
Purchase #7	$155.27	8.296%	$168.1512	$168.15	$168.15	$168.20
7 purchase totals =	$676.91		$743.9446	$743.94	$744.00	$743.90