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	$83.34	7.705%	$89.7613	$89.76	$89.75	$89.80
Purchase #2	$82.60	9.213%	$90.2099	$90.21	$90.20	$90.20
Purchase #3	$66.87	6.700%	$71.3503	$71.35	$71.35	$71.40
Purchase #4	$107.61	3.681%	$111.5711	$111.57	$111.55	$111.60
Purchase #5	$185.77	7.622%	$199.9294	$199.93	$199.95	$199.90
Purchase #6	$178.51	9.142%	$194.8294	$194.83	$194.85	$194.80
Purchase #7	$16.59	3.360%	$17.1474	$17.15	$17.15	$17.10
7 purchase totals =	$721.29		$774.7988	$774.80	$774.80	$774.80