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	$18.58	7.675%	$20.006	$20.01	$20.00	$20.00
Purchase #2	$160.94	11.687%	$179.7491	$179.75	$179.75	$179.70
Purchase #3	$116.59	9.256%	$127.3816	$127.38	$127.40	$127.40
Purchase #4	$168.72	12.762%	$190.252	$190.25	$190.25	$190.30
Purchase #5	$15.50	9.216%	$16.9285	$16.93	$16.95	$16.90
Purchase #6	$104.95	5.660%	$110.8902	$110.89	$110.90	$110.90
Purchase #7	$63.33	4.591%	$66.2375	$66.24	$66.25	$66.20
7 purchase totals =	$648.61		$711.4449	$711.45	$711.50	$711.40