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	$16.90	7.401%	$18.1508	$18.15	$18.15	$18.20
Purchase #2	$49.42	7.110%	$52.9338	$52.93	$52.95	$52.90
Purchase #3	$223.41	3.637%	$231.5354	$231.54	$231.55	$231.50
Purchase #4	$9.95	6.466%	$10.5934	$10.59	$10.60	$10.60
Purchase #5	$126.95	3.674%	$131.6141	$131.61	$131.60	$131.60
Purchase #6	$49.80	7.510%	$53.54	$53.54	$53.55	$53.50
Purchase #7	$250.54	5.325%	$263.8813	$263.88	$263.90	$263.90
7 purchase totals =	$726.97		$762.2488	$762.24	$762.30	$762.20