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	$55.56	13.778%	$63.2151	$63.22	$63.20	$63.20
Purchase #2	$55.52	6.804%	$59.2976	$59.30	$59.30	$59.30
Purchase #3	$47.69	12.626%	$53.7113	$53.71	$53.70	$53.70
Purchase #4	$124.75	12.294%	$140.0868	$140.09	$140.10	$140.10
Purchase #5	$238.38	13.799%	$271.2741	$271.27	$271.25	$271.30
Purchase #6	$172.88	11.847%	$193.3611	$193.36	$193.35	$193.40
Purchase #7	$95.45	10.466%	$105.4398	$105.44	$105.45	$105.40
7 purchase totals =	$790.23		$886.3858	$886.39	$886.35	$886.40