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	$52.66	10.745%	$58.3183	$58.32	$58.30	$58.30
Purchase #2	$170.92	8.518%	$185.479	$185.48	$185.50	$185.50
Purchase #3	$133.52	10.849%	$148.0056	$148.01	$148.00	$148.00
Purchase #4	$58.87	13.599%	$66.8757	$66.88	$66.90	$66.90
Purchase #5	$46.42	4.326%	$48.4281	$48.43	$48.45	$48.40
Purchase #6	$80.59	12.497%	$90.6613	$90.66	$90.65	$90.70
Purchase #7	$167.61	10.759%	$185.6432	$185.64	$185.65	$185.60
7 purchase totals =	$710.59		$783.4112	$783.42	$783.45	$783.40