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	$16.35	12.323%	$18.3648	$18.36	$18.35	$18.40
Purchase #2	$116.87	8.822%	$127.1803	$127.18	$127.20	$127.20
Purchase #3	$120.70	13.107%	$136.5201	$136.52	$136.50	$136.50
Purchase #4	$48.34	5.283%	$50.8938	$50.89	$50.90	$50.90
Purchase #5	$69.41	4.576%	$72.5862	$72.59	$72.60	$72.60
Purchase #6	$160.95	11.348%	$179.2146	$179.21	$179.20	$179.20
Purchase #7	$82.36	8.679%	$89.508	$89.51	$89.50	$89.50
7 purchase totals =	$614.98		$674.2678	$674.26	$674.25	$674.30