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	$60.86	9.274%	$66.5042	$66.50	$66.50	$66.50
Purchase #2	$16.97	9.697%	$18.6156	$18.62	$18.60	$18.60
Purchase #3	$101.57	11.141%	$112.8859	$112.89	$112.90	$112.90
Purchase #4	$193.46	13.676%	$219.9176	$219.92	$219.90	$219.90
Purchase #5	$179.89	7.527%	$193.4303	$193.43	$193.45	$193.40
Purchase #6	$173.56	6.685%	$185.1625	$185.16	$185.15	$185.20
Purchase #7	$231.37	5.404%	$243.8732	$243.87	$243.85	$243.90
7 purchase totals =	$957.68		$1,040.3893	$1,040.39	$1,040.35	$1,040.40