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	$46.79	8.762%	$50.8897	$50.89	$50.90	$50.90
Purchase #2	$10.67	6.397%	$11.3526	$11.35	$11.35	$11.40
Purchase #3	$60.50	8.618%	$65.7139	$65.71	$65.70	$65.70
Purchase #4	$171.33	9.449%	$187.519	$187.52	$187.50	$187.50
Purchase #5	$148.27	13.321%	$168.021	$168.02	$168.00	$168.00
Purchase #6	$12.50	12.688%	$14.086	$14.09	$14.10	$14.10
Purchase #7	$37.95	11.833%	$42.4406	$42.44	$42.45	$42.40
7 purchase totals =	$488.01		$540.0228	$540.02	$540.00	$540.00