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	$10.90	12.121%	$12.2212	$12.22	$12.20	$12.20
Purchase #2	$77.36	6.352%	$82.2739	$82.27	$82.25	$82.30
Purchase #3	$192.44	3.830%	$199.8105	$199.81	$199.80	$199.80
Purchase #4	$82.95	9.358%	$90.7125	$90.71	$90.70	$90.70
Purchase #5	$35.26	10.861%	$39.0896	$39.09	$39.10	$39.10
Purchase #6	$173.37	9.687%	$190.1644	$190.16	$190.15	$190.20
Purchase #7	$88.44	5.714%	$93.4935	$93.49	$93.50	$93.50
7 purchase totals =	$660.72		$707.7656	$707.75	$707.70	$707.80