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	$94.60	5.184%	$99.5041	$99.50	$99.50	$99.50
Purchase #2	$58.92	11.858%	$65.9067	$65.91	$65.90	$65.90
Purchase #3	$59.85	7.781%	$64.5069	$64.51	$64.50	$64.50
Purchase #4	$184.67	8.241%	$199.8887	$199.89	$199.90	$199.90
Purchase #5	$207.80	8.390%	$225.2344	$225.23	$225.25	$225.20
Purchase #6	$115.26	13.216%	$130.4928	$130.49	$130.50	$130.50
Purchase #7	$32.81	5.548%	$34.6303	$34.63	$34.65	$34.60
7 purchase totals =	$753.91		$820.1639	$820.16	$820.20	$820.10