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	$18.29	10.509%	$20.2121	$20.21	$20.20	$20.20
Purchase #2	$82.60	8.268%	$89.4294	$89.43	$89.45	$89.40
Purchase #3	$101.34	5.508%	$106.9218	$106.92	$106.90	$106.90
Purchase #4	$60.50	6.231%	$64.2698	$64.27	$64.25	$64.30
Purchase #5	$34.58	9.385%	$37.8253	$37.83	$37.85	$37.80
Purchase #6	$170.63	11.709%	$190.6091	$190.61	$190.60	$190.60
Purchase #7	$22.46	11.795%	$25.1092	$25.11	$25.10	$25.10
7 purchase totals =	$490.40		$534.3767	$534.38	$534.35	$534.30