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	$46.47	10.218%	$51.2183	$51.22	$51.20	$51.20
Purchase #2	$104.89	6.614%	$111.8274	$111.83	$111.85	$111.80
Purchase #3	$34.92	4.476%	$36.483	$36.48	$36.50	$36.50
Purchase #4	$86.78	5.581%	$91.6232	$91.62	$91.60	$91.60
Purchase #5	$165.95	11.849%	$185.6134	$185.61	$185.60	$185.60
Purchase #6	$21.54	9.689%	$23.627	$23.63	$23.65	$23.60
Purchase #7	$34.74	8.748%	$37.7791	$37.78	$37.80	$37.80
7 purchase totals =	$495.29		$538.1714	$538.17	$538.20	$538.10