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	$70.50	11.744%	$78.7795	$78.78	$78.80	$78.80
Purchase #2	$86.69	7.338%	$93.0513	$93.05	$93.05	$93.10
Purchase #3	$10.83	4.776%	$11.3472	$11.35	$11.35	$11.30
Purchase #4	$39.49	7.353%	$42.3937	$42.39	$42.40	$42.40
Purchase #5	$15.92	3.667%	$16.5038	$16.50	$16.50	$16.50
Purchase #6	$126.78	12.334%	$142.417	$142.42	$142.40	$142.40
Purchase #7	$60.70	10.159%	$66.8665	$66.87	$66.85	$66.90
7 purchase totals =	$410.91		$451.3590	$451.36	$451.35	$451.40