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	$169.74	6.120%	$180.1281	$180.13	$180.15	$180.10
Purchase #2	$166.57	13.791%	$189.5417	$189.54	$189.55	$189.50
Purchase #3	$49.40	10.395%	$54.5351	$54.54	$54.55	$54.50
Purchase #4	$27.36	5.326%	$28.8172	$28.82	$28.80	$28.80
Purchase #5	$129.59	8.651%	$140.8008	$140.80	$140.80	$140.80
Purchase #6	$153.25	12.626%	$172.5993	$172.60	$172.60	$172.60
Purchase #7	$219.40	5.666%	$231.8312	$231.83	$231.85	$231.80
7 purchase totals =	$915.31		$998.2534	$998.26	$998.30	$998.10