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	$81.41	12.412%	$91.5146	$91.51	$91.50	$91.50
Purchase #2	$146.36	6.602%	$156.0227	$156.02	$156.00	$156.00
Purchase #3	$19.37	12.672%	$21.8246	$21.82	$21.80	$21.80
Purchase #4	$239.88	13.829%	$273.053	$273.05	$273.05	$273.10
Purchase #5	$96.53	6.756%	$103.0516	$103.05	$103.05	$103.10
Purchase #6	$141.69	8.397%	$153.5877	$153.59	$153.60	$153.60
Purchase #7	$98.85	12.432%	$111.139	$111.14	$111.15	$111.10
7 purchase totals =	$824.09		$910.1932	$910.18	$910.15	$910.20