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	$164.93	3.873%	$171.3177	$171.32	$171.30	$171.30
Purchase #2	$49.40	6.821%	$52.7696	$52.77	$52.75	$52.80
Purchase #3	$42.53	3.280%	$43.925	$43.93	$43.95	$43.90
Purchase #4	$217.29	10.153%	$239.3515	$239.35	$239.35	$239.40
Purchase #5	$172.57	13.225%	$195.3924	$195.39	$195.40	$195.40
Purchase #6	$98.47	13.337%	$111.6029	$111.60	$111.60	$111.60
Purchase #7	$30.26	4.764%	$31.7016	$31.70	$31.70	$31.70
7 purchase totals =	$775.45		$846.0607	$846.06	$846.05	$846.10