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	$249.40	11.208%	$277.3528	$277.35	$277.35	$277.40
Purchase #2	$246.75	3.273%	$254.8261	$254.83	$254.85	$254.80
Purchase #3	$96.68	7.159%	$103.6013	$103.60	$103.60	$103.60
Purchase #4	$175.71	10.480%	$194.1244	$194.12	$194.10	$194.10
Purchase #5	$206.25	4.772%	$216.0923	$216.09	$216.10	$216.10
Purchase #6	$94.36	9.718%	$103.5299	$103.53	$103.55	$103.50
Purchase #7	$57.62	3.199%	$59.4633	$59.46	$59.45	$59.50
7 purchase totals =	$1,126.77		$1,208.9901	$1,208.98	$1,209.00	$1,209.00