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	$9.61	10.405%	$10.6099	$10.61	$10.60	$10.60
Purchase #2	$197.88	9.371%	$216.4233	$216.42	$216.40	$216.40
Purchase #3	$133.25	7.718%	$143.5342	$143.53	$143.55	$143.50
Purchase #4	$110.40	11.772%	$123.3963	$123.40	$123.40	$123.40
Purchase #5	$61.32	4.256%	$63.9298	$63.93	$63.95	$63.90
Purchase #6	$94.97	11.174%	$105.5819	$105.58	$105.60	$105.60
Purchase #7	$232.89	7.637%	$250.6758	$250.68	$250.70	$250.70
7 purchase totals =	$840.32		$914.1512	$914.15	$914.20	$914.10