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	$131.32	9.786%	$144.171	$144.17	$144.15	$144.20
Purchase #2	$128.83	8.246%	$139.4533	$139.45	$139.45	$139.50
Purchase #3	$153.65	5.808%	$162.574	$162.57	$162.55	$162.60
Purchase #4	$218.78	10.650%	$242.0801	$242.08	$242.10	$242.10
Purchase #5	$76.93	11.229%	$85.5685	$85.57	$85.55	$85.60
Purchase #6	$14.64	5.177%	$15.3979	$15.40	$15.40	$15.40
Purchase #7	$44.49	4.111%	$46.319	$46.32	$46.30	$46.30
7 purchase totals =	$768.64		$835.5638	$835.56	$835.50	$835.70