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	$47.50	12.596%	$53.4831	$53.48	$53.50	$53.50
Purchase #2	$244.54	8.681%	$265.7685	$265.77	$265.75	$265.80
Purchase #3	$183.73	3.668%	$190.4692	$190.47	$190.45	$190.50
Purchase #4	$15.88	10.861%	$17.6047	$17.60	$17.60	$17.60
Purchase #5	$24.26	4.546%	$25.3629	$25.36	$25.35	$25.40
Purchase #6	$171.82	10.853%	$190.4676	$190.47	$190.45	$190.50
Purchase #7	$33.93	8.300%	$36.7462	$36.75	$36.75	$36.70
7 purchase totals =	$721.66		$779.9022	$779.90	$779.85	$780.00