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	$105.88	6.166%	$112.4086	$112.41	$112.40	$112.40
Purchase #2	$110.89	10.555%	$122.5944	$122.59	$122.60	$122.60
Purchase #3	$54.37	13.285%	$61.5931	$61.59	$61.60	$61.60
Purchase #4	$93.46	11.652%	$104.35	$104.35	$104.35	$104.40
Purchase #5	$210.80	7.864%	$227.3773	$227.38	$227.40	$227.40
Purchase #6	$66.60	4.508%	$69.6023	$69.60	$69.60	$69.60
Purchase #7	$28.65	12.139%	$32.1278	$32.13	$32.15	$32.10
7 purchase totals =	$670.65		$730.0535	$730.05	$730.10	$730.10