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	$80.77	7.181%	$86.5701	$86.57	$86.55	$86.60
Purchase #2	$250.72	9.562%	$274.6938	$274.69	$274.70	$274.70
Purchase #3	$143.61	6.689%	$153.2161	$153.22	$153.20	$153.20
Purchase #4	$81.38	13.345%	$92.2402	$92.24	$92.25	$92.20
Purchase #5	$12.55	10.667%	$13.8887	$13.89	$13.90	$13.90
Purchase #6	$53.45	12.204%	$59.973	$59.97	$59.95	$60.00
Purchase #7	$35.99	5.325%	$37.9065	$37.91	$37.90	$37.90
7 purchase totals =	$658.47		$718.4884	$718.49	$718.45	$718.50