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	$220.85	12.354%	$248.1338	$248.13	$248.15	$248.10
Purchase #2	$180.85	10.240%	$199.369	$199.37	$199.35	$199.40
Purchase #3	$230.93	13.652%	$262.4566	$262.46	$262.45	$262.50
Purchase #4	$37.57	4.849%	$39.3918	$39.39	$39.40	$39.40
Purchase #5	$198.89	13.440%	$225.6208	$225.62	$225.60	$225.60
Purchase #6	$11.94	4.370%	$12.4618	$12.46	$12.45	$12.50
Purchase #7	$28.31	10.734%	$31.3488	$31.35	$31.35	$31.30
7 purchase totals =	$909.34		$1,018.7826	$1,018.78	$1,018.75	$1,018.80