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	$78.28	4.565%	$81.8535	$81.85	$81.85	$81.90
Purchase #2	$38.70	5.834%	$40.9578	$40.96	$40.95	$41.00
Purchase #3	$158.48	3.726%	$164.385	$164.39	$164.40	$164.40
Purchase #4	$141.65	7.816%	$152.7214	$152.72	$152.70	$152.70
Purchase #5	$206.28	12.748%	$232.5766	$232.58	$232.60	$232.60
Purchase #6	$40.40	8.369%	$43.7811	$43.78	$43.80	$43.80
Purchase #7	$46.93	3.123%	$48.3956	$48.40	$48.40	$48.40
7 purchase totals =	$710.72		$764.6710	$764.68	$764.70	$764.80