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	$30.33	10.728%	$33.5838	$33.58	$33.60	$33.60
Purchase #2	$33.79	9.365%	$36.9544	$36.95	$36.95	$37.00
Purchase #3	$185.69	7.634%	$199.8656	$199.87	$199.85	$199.90
Purchase #4	$206.98	5.375%	$218.1052	$218.11	$218.10	$218.10
Purchase #5	$175.79	3.219%	$181.4487	$181.45	$181.45	$181.40
Purchase #6	$99.60	12.225%	$111.7761	$111.78	$111.80	$111.80
Purchase #7	$50.79	13.451%	$57.6218	$57.62	$57.60	$57.60
7 purchase totals =	$782.97		$839.3556	$839.36	$839.35	$839.40