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	$16.33	13.705%	$18.568	$18.57	$18.55	$18.60
Purchase #2	$80.84	9.596%	$88.5974	$88.60	$88.60	$88.60
Purchase #3	$183.85	9.754%	$201.7827	$201.78	$201.80	$201.80
Purchase #4	$78.32	4.629%	$81.9454	$81.95	$81.95	$81.90
Purchase #5	$59.74	11.674%	$66.714	$66.71	$66.70	$66.70
Purchase #6	$38.86	3.710%	$40.3017	$40.30	$40.30	$40.30
Purchase #7	$82.31	8.598%	$89.387	$89.39	$89.40	$89.40
7 purchase totals =	$540.25		$587.2962	$587.30	$587.30	$587.30