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	$235.61	9.130%	$257.1212	$257.12	$257.10	$257.10
Purchase #2	$161.89	9.102%	$176.6252	$176.63	$176.65	$176.60
Purchase #3	$29.80	3.323%	$30.7903	$30.79	$30.80	$30.80
Purchase #4	$150.38	11.509%	$167.6872	$167.69	$167.70	$167.70
Purchase #5	$82.92	7.473%	$89.1166	$89.12	$89.10	$89.10
Purchase #6	$16.52	13.239%	$18.7071	$18.71	$18.70	$18.70
Purchase #7	$106.35	4.590%	$111.2315	$111.23	$111.25	$111.20
7 purchase totals =	$783.47		$851.2791	$851.29	$851.30	$851.20