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	$96.52	13.835%	$109.8735	$109.87	$109.85	$109.90
Purchase #2	$246.49	12.710%	$277.8189	$277.82	$277.80	$277.80
Purchase #3	$132.80	7.321%	$142.5223	$142.52	$142.50	$142.50
Purchase #4	$91.54	8.543%	$99.3603	$99.36	$99.35	$99.40
Purchase #5	$9.28	12.671%	$10.4559	$10.46	$10.45	$10.50
Purchase #6	$201.38	12.699%	$226.9532	$226.95	$226.95	$227.00
Purchase #7	$207.67	7.271%	$222.7697	$222.77	$222.75	$222.80
7 purchase totals =	$985.68		$1,089.7538	$1,089.75	$1,089.65	$1,089.90