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	$67.71	7.606%	$72.86	$72.86	$72.85	$72.90
Purchase #2	$129.65	11.376%	$144.399	$144.40	$144.40	$144.40
Purchase #3	$44.60	8.797%	$48.5235	$48.52	$48.50	$48.50
Purchase #4	$22.50	13.660%	$25.5735	$25.57	$25.55	$25.60
Purchase #5	$51.97	11.276%	$57.8301	$57.83	$57.85	$57.80
Purchase #6	$63.32	12.339%	$71.1331	$71.13	$71.15	$71.10
Purchase #7	$112.59	3.464%	$116.4901	$116.49	$116.50	$116.50
7 purchase totals =	$492.34		$536.8093	$536.80	$536.80	$536.80