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	$144.78	13.603%	$164.4744	$164.47	$164.45	$164.50
Purchase #2	$26.70	13.828%	$30.3921	$30.39	$30.40	$30.40
Purchase #3	$136.37	4.261%	$142.1807	$142.18	$142.20	$142.20
Purchase #4	$221.46	8.297%	$239.8345	$239.83	$239.85	$239.80
Purchase #5	$54.53	3.351%	$56.3573	$56.36	$56.35	$56.40
Purchase #6	$100.80	8.753%	$109.623	$109.62	$109.60	$109.60
Purchase #7	$33.69	10.751%	$37.312	$37.31	$37.30	$37.30
7 purchase totals =	$718.33		$780.1740	$780.16	$780.15	$780.20