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	$18.42	8.811%	$20.043	$20.04	$20.05	$20.00
Purchase #2	$231.44	6.278%	$245.9698	$245.97	$245.95	$246.00
Purchase #3	$90.79	9.128%	$99.0773	$99.08	$99.10	$99.10
Purchase #4	$151.43	12.649%	$170.5844	$170.58	$170.60	$170.60
Purchase #5	$59.51	9.836%	$65.3634	$65.36	$65.35	$65.40
Purchase #6	$82.49	8.395%	$89.415	$89.42	$89.40	$89.40
Purchase #7	$218.52	10.442%	$241.3379	$241.34	$241.35	$241.30
7 purchase totals =	$852.60		$931.7908	$931.79	$931.80	$931.80