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	$13.27	4.534%	$13.8717	$13.87	$13.85	$13.90
Purchase #2	$208.82	10.319%	$230.3681	$230.37	$230.35	$230.40
Purchase #3	$36.94	4.449%	$38.5835	$38.58	$38.60	$38.60
Purchase #4	$50.85	7.869%	$54.8514	$54.85	$54.85	$54.90
Purchase #5	$37.61	3.460%	$38.9113	$38.91	$38.90	$38.90
Purchase #6	$223.49	3.614%	$231.5669	$231.57	$231.55	$231.60
Purchase #7	$208.89	5.428%	$220.2285	$220.23	$220.25	$220.20
7 purchase totals =	$779.87		$828.3814	$828.38	$828.35	$828.50