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	$48.58	12.775%	$54.7861	$54.79	$54.80	$54.80
Purchase #2	$170.39	12.240%	$191.2457	$191.25	$191.25	$191.20
Purchase #3	$237.27	10.496%	$262.1739	$262.17	$262.15	$262.20
Purchase #4	$47.91	11.359%	$53.3521	$53.35	$53.35	$53.40
Purchase #5	$37.70	7.392%	$40.4868	$40.49	$40.50	$40.50
Purchase #6	$156.54	4.698%	$163.8942	$163.89	$163.90	$163.90
Purchase #7	$180.27	10.308%	$198.8522	$198.85	$198.85	$198.90
7 purchase totals =	$878.66		$964.7910	$964.79	$964.80	$964.90