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	$38.37	11.515%	$42.7883	$42.79	$42.80	$42.80
Purchase #2	$149.82	8.420%	$162.4348	$162.43	$162.45	$162.40
Purchase #3	$136.83	7.323%	$146.8501	$146.85	$146.85	$146.90
Purchase #4	$18.84	10.711%	$20.858	$20.86	$20.85	$20.90
Purchase #5	$99.44	4.457%	$103.872	$103.87	$103.85	$103.90
Purchase #6	$93.32	7.659%	$100.4674	$100.47	$100.45	$100.50
Purchase #7	$52.90	11.105%	$58.7745	$58.77	$58.75	$58.80
7 purchase totals =	$589.52		$636.0451	$636.04	$636.00	$636.20