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	$240.82	4.350%	$251.2957	$251.30	$251.30	$251.30
Purchase #2	$60.25	10.320%	$66.4678	$66.47	$66.45	$66.50
Purchase #3	$65.73	7.371%	$70.575	$70.58	$70.60	$70.60
Purchase #4	$38.34	7.657%	$41.2757	$41.28	$41.30	$41.30
Purchase #5	$219.48	3.670%	$227.5349	$227.53	$227.55	$227.50
Purchase #6	$227.91	7.853%	$245.8078	$245.81	$245.80	$245.80
Purchase #7	$80.63	11.444%	$89.8573	$89.86	$89.85	$89.90
7 purchase totals =	$933.16		$992.8142	$992.83	$992.85	$992.90