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	$17.47	3.735%	$18.1225	$18.12	$18.10	$18.10
Purchase #2	$64.89	5.212%	$68.2721	$68.27	$68.25	$68.30
Purchase #3	$50.61	7.229%	$54.2686	$54.27	$54.25	$54.30
Purchase #4	$191.75	7.175%	$205.5081	$205.51	$205.50	$205.50
Purchase #5	$80.40	12.123%	$90.1469	$90.15	$90.15	$90.10
Purchase #6	$155.66	10.330%	$171.7397	$171.74	$171.75	$171.70
Purchase #7	$119.66	12.293%	$134.3698	$134.37	$134.35	$134.40
7 purchase totals =	$680.44		$742.4277	$742.43	$742.35	$742.40