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	$75.42	6.640%	$80.4279	$80.43	$80.45	$80.40
Purchase #2	$7.40	3.487%	$7.658	$7.66	$7.65	$7.70
Purchase #3	$246.79	7.490%	$265.2746	$265.27	$265.25	$265.30
Purchase #4	$32.68	11.773%	$36.5274	$36.53	$36.55	$36.50
Purchase #5	$81.53	10.516%	$90.1037	$90.10	$90.10	$90.10
Purchase #6	$29.27	8.798%	$31.8452	$31.85	$31.85	$31.80
Purchase #7	$157.36	5.874%	$166.6033	$166.60	$166.60	$166.60
7 purchase totals =	$630.45		$678.4401	$678.44	$678.45	$678.40