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	$70.46	4.485%	$73.6201	$73.62	$73.60	$73.60
Purchase #2	$117.32	7.689%	$126.3407	$126.34	$126.35	$126.30
Purchase #3	$93.51	7.542%	$100.5625	$100.56	$100.55	$100.60
Purchase #4	$164.63	9.510%	$180.2863	$180.29	$180.30	$180.30
Purchase #5	$133.77	9.764%	$146.8313	$146.83	$146.85	$146.80
Purchase #6	$158.45	6.511%	$168.7667	$168.77	$168.75	$168.80
Purchase #7	$181.69	11.691%	$202.9314	$202.93	$202.95	$202.90
7 purchase totals =	$919.83		$999.3390	$999.34	$999.35	$999.30