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	$182.39	12.568%	$205.3128	$205.31	$205.30	$205.30
Purchase #2	$41.42	8.827%	$45.0761	$45.08	$45.10	$45.10
Purchase #3	$147.76	13.218%	$167.2909	$167.29	$167.30	$167.30
Purchase #4	$33.82	11.658%	$37.7627	$37.76	$37.75	$37.80
Purchase #5	$183.41	8.122%	$198.3066	$198.31	$198.30	$198.30
Purchase #6	$132.56	5.801%	$140.2498	$140.25	$140.25	$140.20
Purchase #7	$23.67	3.295%	$24.4499	$24.45	$24.45	$24.40
7 purchase totals =	$745.03		$818.4488	$818.45	$818.45	$818.40