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	$26.56	8.613%	$28.8476	$28.85	$28.85	$28.80
Purchase #2	$170.89	12.746%	$192.6716	$192.67	$192.65	$192.70
Purchase #3	$241.26	8.357%	$261.4221	$261.42	$261.40	$261.40
Purchase #4	$72.89	11.182%	$81.0406	$81.04	$81.05	$81.00
Purchase #5	$238.83	13.796%	$271.779	$271.78	$271.80	$271.80
Purchase #6	$142.72	6.598%	$152.1367	$152.14	$152.15	$152.10
Purchase #7	$24.88	11.705%	$27.7922	$27.79	$27.80	$27.80
7 purchase totals =	$918.03		$1,015.6898	$1,015.69	$1,015.70	$1,015.60