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	$104.97	13.589%	$119.2344	$119.23	$119.25	$119.20
Purchase #2	$165.59	8.347%	$179.4118	$179.41	$179.40	$179.40
Purchase #3	$101.30	3.861%	$105.2112	$105.21	$105.20	$105.20
Purchase #4	$152.35	7.753%	$164.1617	$164.16	$164.15	$164.20
Purchase #5	$79.45	13.522%	$90.1932	$90.19	$90.20	$90.20
Purchase #6	$81.78	5.623%	$86.3785	$86.38	$86.40	$86.40
Purchase #7	$95.37	4.458%	$99.6216	$99.62	$99.60	$99.60
7 purchase totals =	$780.81		$844.2124	$844.20	$844.20	$844.20