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	$33.39	13.741%	$37.9781	$37.98	$38.00	$38.00
Purchase #2	$82.72	10.313%	$91.2509	$91.25	$91.25	$91.30
Purchase #3	$151.45	11.847%	$169.3923	$169.39	$169.40	$169.40
Purchase #4	$83.35	12.619%	$93.8679	$93.87	$93.85	$93.90
Purchase #5	$132.53	6.332%	$140.9218	$140.92	$140.90	$140.90
Purchase #6	$80.86	11.177%	$89.8977	$89.90	$89.90	$89.90
Purchase #7	$23.78	5.747%	$25.1466	$25.15	$25.15	$25.10
7 purchase totals =	$588.08		$648.4553	$648.46	$648.45	$648.50