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	$66.30	8.870%	$72.1808	$72.18	$72.20	$72.20
Purchase #2	$231.74	4.364%	$241.8531	$241.85	$241.85	$241.90
Purchase #3	$188.48	11.176%	$209.5445	$209.54	$209.55	$209.50
Purchase #4	$163.55	10.326%	$180.4382	$180.44	$180.45	$180.40
Purchase #5	$94.89	12.360%	$106.6184	$106.62	$106.60	$106.60
Purchase #6	$121.41	7.239%	$130.1989	$130.20	$130.20	$130.20
Purchase #7	$33.44	12.508%	$37.6227	$37.62	$37.60	$37.60
7 purchase totals =	$899.81		$978.4566	$978.45	$978.45	$978.40