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	$245.28	5.255%	$258.1695	$258.17	$258.15	$258.20
Purchase #2	$89.92	8.376%	$97.4517	$97.45	$97.45	$97.50
Purchase #3	$52.60	6.499%	$56.0185	$56.02	$56.00	$56.00
Purchase #4	$233.50	9.841%	$256.4787	$256.48	$256.50	$256.50
Purchase #5	$16.87	9.659%	$18.4995	$18.50	$18.50	$18.50
Purchase #6	$130.91	12.221%	$146.9085	$146.91	$146.90	$146.90
Purchase #7	$140.81	8.155%	$152.2931	$152.29	$152.30	$152.30
7 purchase totals =	$909.89		$985.8195	$985.82	$985.80	$985.90