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	$9.32	5.405%	$9.8237	$9.82	$9.80	$9.80
Purchase #2	$70.60	12.440%	$79.3826	$79.38	$79.40	$79.40
Purchase #3	$67.39	13.740%	$76.6494	$76.65	$76.65	$76.60
Purchase #4	$87.98	8.565%	$95.5155	$95.52	$95.50	$95.50
Purchase #5	$84.56	5.786%	$89.4526	$89.45	$89.45	$89.50
Purchase #6	$127.28	10.282%	$140.3669	$140.37	$140.35	$140.40
Purchase #7	$153.97	9.856%	$169.1453	$169.15	$169.15	$169.10
7 purchase totals =	$601.10		$660.3360	$660.34	$660.30	$660.30