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	$104.57	7.566%	$112.4818	$112.48	$112.50	$112.50
Purchase #2	$16.69	10.346%	$18.4167	$18.42	$18.40	$18.40
Purchase #3	$18.56	12.205%	$20.8252	$20.83	$20.85	$20.80
Purchase #4	$15.79	13.752%	$17.9614	$17.96	$17.95	$18.00
Purchase #5	$68.85	5.675%	$72.7572	$72.76	$72.75	$72.80
Purchase #6	$205.35	5.258%	$216.1473	$216.15	$216.15	$216.10
Purchase #7	$29.71	4.737%	$31.1174	$31.12	$31.10	$31.10
7 purchase totals =	$459.52		$489.7070	$489.72	$489.70	$489.70