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	$134.87	11.646%	$150.577	$150.58	$150.60	$150.60
Purchase #2	$81.34	10.766%	$90.0971	$90.10	$90.10	$90.10
Purchase #3	$15.86	6.118%	$16.8303	$16.83	$16.85	$16.80
Purchase #4	$145.33	10.295%	$160.2917	$160.29	$160.30	$160.30
Purchase #5	$221.54	6.388%	$235.692	$235.69	$235.70	$235.70
Purchase #6	$79.52	3.712%	$82.4718	$82.47	$82.45	$82.50
Purchase #7	$95.92	11.480%	$106.9316	$106.93	$106.95	$106.90
7 purchase totals =	$774.38		$842.8915	$842.89	$842.95	$842.90