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	$54.77	10.613%	$60.5827	$60.58	$60.60	$60.60
Purchase #2	$52.67	5.250%	$55.4352	$55.44	$55.45	$55.40
Purchase #3	$143.90	13.211%	$162.9106	$162.91	$162.90	$162.90
Purchase #4	$35.70	6.235%	$37.9259	$37.93	$37.95	$37.90
Purchase #5	$83.27	10.576%	$92.0766	$92.08	$92.10	$92.10
Purchase #6	$64.78	10.804%	$71.7788	$71.78	$71.80	$71.80
Purchase #7	$194.39	5.811%	$205.686	$205.69	$205.70	$205.70
7 purchase totals =	$629.48		$686.3958	$686.41	$686.50	$686.40