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	$13.72	6.519%	$14.6144	$14.61	$14.60	$14.60
Purchase #2	$223.88	9.624%	$245.4262	$245.43	$245.45	$245.40
Purchase #3	$160.92	11.776%	$179.8699	$179.87	$179.85	$179.90
Purchase #4	$38.39	8.789%	$41.7641	$41.76	$41.75	$41.80
Purchase #5	$99.60	3.734%	$103.3191	$103.32	$103.30	$103.30
Purchase #6	$209.58	9.772%	$230.0602	$230.06	$230.05	$230.10
Purchase #7	$151.66	11.176%	$168.6095	$168.61	$168.60	$168.60
7 purchase totals =	$897.75		$983.6634	$983.66	$983.60	$983.70