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	$80.67	12.392%	$90.6666	$90.67	$90.65	$90.70
Purchase #2	$245.40	5.739%	$259.4835	$259.48	$259.50	$259.50
Purchase #3	$90.50	3.454%	$93.6259	$93.63	$93.65	$93.60
Purchase #4	$142.33	12.412%	$159.996	$160.00	$160.00	$160.00
Purchase #5	$149.51	8.535%	$162.2707	$162.27	$162.25	$162.30
Purchase #6	$14.45	5.240%	$15.2072	$15.21	$15.20	$15.20
Purchase #7	$52.46	13.325%	$59.4503	$59.45	$59.45	$59.50
7 purchase totals =	$775.32		$840.7002	$840.71	$840.70	$840.80