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	$27.66	5.657%	$29.2247	$29.22	$29.20	$29.20
Purchase #2	$229.59	5.813%	$242.9361	$242.94	$242.95	$242.90
Purchase #3	$18.39	13.589%	$20.889	$20.89	$20.90	$20.90
Purchase #4	$75.78	6.105%	$80.4064	$80.41	$80.40	$80.40
Purchase #5	$23.35	10.606%	$25.8265	$25.83	$25.85	$25.80
Purchase #6	$230.52	12.719%	$259.8398	$259.84	$259.85	$259.80
Purchase #7	$159.57	5.338%	$168.0878	$168.09	$168.10	$168.10
7 purchase totals =	$764.86		$827.2103	$827.22	$827.25	$827.10