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	$51.48	9.538%	$56.3902	$56.39	$56.40	$56.40
Purchase #2	$136.71	7.479%	$146.9345	$146.93	$146.95	$146.90
Purchase #3	$58.61	13.472%	$66.5059	$66.51	$66.50	$66.50
Purchase #4	$210.70	13.116%	$238.3354	$238.34	$238.35	$238.30
Purchase #5	$168.28	4.218%	$175.3781	$175.38	$175.40	$175.40
Purchase #6	$77.68	7.273%	$83.3297	$83.33	$83.35	$83.30
Purchase #7	$97.40	5.144%	$102.4103	$102.41	$102.40	$102.40
7 purchase totals =	$800.86		$869.2841	$869.29	$869.35	$869.20