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	$109.37	9.354%	$119.6005	$119.60	$119.60	$119.60
Purchase #2	$52.55	12.597%	$59.1697	$59.17	$59.15	$59.20
Purchase #3	$243.46	8.575%	$264.3367	$264.34	$264.35	$264.30
Purchase #4	$66.43	6.770%	$70.9273	$70.93	$70.95	$70.90
Purchase #5	$178.89	5.493%	$188.7164	$188.72	$188.70	$188.70
Purchase #6	$45.88	8.730%	$49.8853	$49.89	$49.90	$49.90
Purchase #7	$12.77	10.810%	$14.1504	$14.15	$14.15	$14.20
7 purchase totals =	$709.35		$766.7863	$766.80	$766.80	$766.80