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	$236.45	12.215%	$265.3324	$265.33	$265.35	$265.30
Purchase #2	$49.42	6.165%	$52.4667	$52.47	$52.45	$52.50
Purchase #3	$81.56	9.747%	$89.5097	$89.51	$89.50	$89.50
Purchase #4	$66.64	12.354%	$74.8727	$74.87	$74.85	$74.90
Purchase #5	$218.59	8.144%	$236.392	$236.39	$236.40	$236.40
Purchase #6	$158.90	3.675%	$164.7396	$164.74	$164.75	$164.70
Purchase #7	$87.30	13.182%	$98.8079	$98.81	$98.80	$98.80
7 purchase totals =	$898.86		$982.1210	$982.12	$982.10	$982.10