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	$123.74	3.648%	$128.254	$128.25	$128.25	$128.30
Purchase #2	$249.35	3.788%	$258.7954	$258.80	$258.80	$258.80
Purchase #3	$178.94	7.169%	$191.7682	$191.77	$191.75	$191.80
Purchase #4	$111.37	8.320%	$120.636	$120.64	$120.65	$120.60
Purchase #5	$245.75	10.698%	$272.0403	$272.04	$272.05	$272.00
Purchase #6	$80.59	11.798%	$90.098	$90.10	$90.10	$90.10
Purchase #7	$83.30	3.246%	$86.0039	$86.00	$86.00	$86.00
7 purchase totals =	$1,073.04		$1,147.5958	$1,147.60	$1,147.60	$1,147.60