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	$132.97	7.269%	$142.6356	$142.64	$142.65	$142.60
Purchase #2	$130.65	13.337%	$148.0748	$148.07	$148.05	$148.10
Purchase #3	$210.95	13.777%	$240.0126	$240.01	$240.00	$240.00
Purchase #4	$14.94	3.558%	$15.4716	$15.47	$15.45	$15.50
Purchase #5	$32.84	13.854%	$37.3897	$37.39	$37.40	$37.40
Purchase #6	$132.38	10.723%	$146.5751	$146.58	$146.60	$146.60
Purchase #7	$144.70	3.822%	$150.2304	$150.23	$150.25	$150.20
7 purchase totals =	$799.43		$880.3898	$880.39	$880.40	$880.40