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	$30.62	12.795%	$34.5378	$34.54	$34.55	$34.50
Purchase #2	$139.69	4.444%	$145.8978	$145.90	$145.90	$145.90
Purchase #3	$247.83	7.194%	$265.6589	$265.66	$265.65	$265.70
Purchase #4	$53.91	10.828%	$59.7474	$59.75	$59.75	$59.70
Purchase #5	$228.80	9.615%	$250.7991	$250.80	$250.80	$250.80
Purchase #6	$169.89	13.489%	$192.8065	$192.81	$192.80	$192.80
Purchase #7	$92.58	12.396%	$104.0562	$104.06	$104.05	$104.10
7 purchase totals =	$963.32		$1,053.5037	$1,053.52	$1,053.50	$1,053.50