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	$163.65	5.434%	$172.5427	$172.54	$172.55	$172.50
Purchase #2	$223.25	8.632%	$242.5209	$242.52	$242.50	$242.50
Purchase #3	$226.97	3.444%	$234.7868	$234.79	$234.80	$234.80
Purchase #4	$33.71	12.224%	$37.8307	$37.83	$37.85	$37.80
Purchase #5	$130.92	5.744%	$138.44	$138.44	$138.45	$138.40
Purchase #6	$131.85	12.714%	$148.6134	$148.61	$148.60	$148.60
Purchase #7	$121.52	5.739%	$128.494	$128.49	$128.50	$128.50
7 purchase totals =	$1,031.87		$1,103.2285	$1,103.22	$1,103.25	$1,103.10