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	$93.94	9.725%	$103.0757	$103.08	$103.10	$103.10
Purchase #2	$19.56	6.113%	$20.7557	$20.76	$20.75	$20.80
Purchase #3	$146.57	10.567%	$162.0581	$162.06	$162.05	$162.10
Purchase #4	$39.43	10.860%	$43.7121	$43.71	$43.70	$43.70
Purchase #5	$57.79	8.108%	$62.4756	$62.48	$62.50	$62.50
Purchase #6	$242.49	4.149%	$252.5509	$252.55	$252.55	$252.60
Purchase #7	$162.64	3.802%	$168.8236	$168.82	$168.80	$168.80
7 purchase totals =	$762.42		$813.4517	$813.46	$813.45	$813.60