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	$58.50	13.379%	$66.3267	$66.33	$66.35	$66.30
Purchase #2	$60.44	4.710%	$63.2867	$63.29	$63.30	$63.30
Purchase #3	$99.71	12.592%	$112.2655	$112.27	$112.25	$112.30
Purchase #4	$13.36	11.199%	$14.8562	$14.86	$14.85	$14.90
Purchase #5	$47.81	12.235%	$53.6596	$53.66	$53.65	$53.70
Purchase #6	$193.56	3.543%	$200.4178	$200.42	$200.40	$200.40
Purchase #7	$166.47	11.431%	$185.4992	$185.50	$185.50	$185.50
7 purchase totals =	$639.85		$696.3117	$696.33	$696.30	$696.40