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	$123.64	13.178%	$139.9333	$139.93	$139.95	$139.90
Purchase #2	$70.60	11.561%	$78.7621	$78.76	$78.75	$78.80
Purchase #3	$49.90	11.682%	$55.7293	$55.73	$55.75	$55.70
Purchase #4	$117.93	5.103%	$123.948	$123.95	$123.95	$123.90
Purchase #5	$171.54	7.715%	$184.7743	$184.77	$184.75	$184.80
Purchase #6	$224.45	9.415%	$245.582	$245.58	$245.60	$245.60
Purchase #7	$46.91	10.111%	$51.6531	$51.65	$51.65	$51.70
7 purchase totals =	$804.97		$880.3821	$880.37	$880.40	$880.40