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	$187.82	12.240%	$210.8092	$210.81	$210.80	$210.80
Purchase #2	$136.47	8.254%	$147.7342	$147.73	$147.75	$147.70
Purchase #3	$14.37	4.870%	$15.0698	$15.07	$15.05	$15.10
Purchase #4	$245.48	4.114%	$255.579	$255.58	$255.60	$255.60
Purchase #5	$112.57	13.570%	$127.8457	$127.85	$127.85	$127.80
Purchase #6	$65.82	10.193%	$72.529	$72.53	$72.55	$72.50
Purchase #7	$27.85	6.107%	$29.5508	$29.55	$29.55	$29.60
7 purchase totals =	$790.38		$859.1177	$859.12	$859.15	$859.10