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	$11.31	12.444%	$12.7174	$12.72	$12.70	$12.70
Purchase #2	$156.88	12.264%	$176.1198	$176.12	$176.10	$176.10
Purchase #3	$141.75	3.243%	$146.347	$146.35	$146.35	$146.30
Purchase #4	$109.45	3.637%	$113.4307	$113.43	$113.45	$113.40
Purchase #5	$171.57	11.256%	$190.8819	$190.88	$190.90	$190.90
Purchase #6	$78.72	10.364%	$86.8785	$86.88	$86.90	$86.90
Purchase #7	$19.71	7.542%	$21.1965	$21.20	$21.20	$21.20
7 purchase totals =	$689.39		$747.5718	$747.58	$747.60	$747.50