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	$76.97	7.286%	$82.578	$82.58	$82.60	$82.60
Purchase #2	$197.87	9.217%	$216.1077	$216.11	$216.10	$216.10
Purchase #3	$34.74	5.170%	$36.5361	$36.54	$36.55	$36.50
Purchase #4	$215.78	12.362%	$242.4547	$242.45	$242.45	$242.50
Purchase #5	$43.81	4.233%	$45.6645	$45.66	$45.65	$45.70
Purchase #6	$57.34	8.286%	$62.0912	$62.09	$62.10	$62.10
Purchase #7	$86.78	4.371%	$90.5732	$90.57	$90.55	$90.60
7 purchase totals =	$713.29		$776.0054	$776.00	$776.00	$776.10