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	$67.60	4.495%	$70.6386	$70.64	$70.65	$70.60
Purchase #2	$134.38	13.761%	$152.872	$152.87	$152.85	$152.90
Purchase #3	$34.71	4.216%	$36.1734	$36.17	$36.15	$36.20
Purchase #4	$200.78	10.836%	$222.5365	$222.54	$222.55	$222.50
Purchase #5	$138.25	12.282%	$155.2299	$155.23	$155.25	$155.20
Purchase #6	$45.26	12.214%	$50.7881	$50.79	$50.80	$50.80
Purchase #7	$80.77	12.352%	$90.7467	$90.75	$90.75	$90.70
7 purchase totals =	$701.75		$778.9852	$778.99	$779.00	$778.90