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	$26.26	9.633%	$28.7896	$28.79	$28.80	$28.80
Purchase #2	$137.50	9.357%	$150.3659	$150.37	$150.35	$150.40
Purchase #3	$77.93	10.285%	$85.9451	$85.95	$85.95	$85.90
Purchase #4	$145.75	8.806%	$158.5847	$158.58	$158.60	$158.60
Purchase #5	$86.69	10.635%	$95.9095	$95.91	$95.90	$95.90
Purchase #6	$141.93	4.610%	$148.473	$148.47	$148.45	$148.50
Purchase #7	$81.45	7.282%	$87.3812	$87.38	$87.40	$87.40
7 purchase totals =	$697.51		$755.4490	$755.45	$755.45	$755.50