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	$77.28	5.693%	$81.6796	$81.68	$81.70	$81.70
Purchase #2	$130.95	9.654%	$143.5919	$143.59	$143.60	$143.60
Purchase #3	$123.93	12.229%	$139.0854	$139.09	$139.10	$139.10
Purchase #4	$210.97	10.862%	$233.8856	$233.89	$233.90	$233.90
Purchase #5	$70.57	11.419%	$78.6284	$78.63	$78.65	$78.60
Purchase #6	$35.52	4.368%	$37.0715	$37.07	$37.05	$37.10
Purchase #7	$5.76	13.102%	$6.5147	$6.51	$6.50	$6.50
7 purchase totals =	$654.98		$720.4571	$720.46	$720.50	$720.50