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	$88.52	13.622%	$100.5782	$100.58	$100.60	$100.60
Purchase #2	$196.97	12.865%	$222.3102	$222.31	$222.30	$222.30
Purchase #3	$233.67	7.701%	$251.6649	$251.66	$251.65	$251.70
Purchase #4	$191.33	13.256%	$216.6927	$216.69	$216.70	$216.70
Purchase #5	$103.65	5.125%	$108.9621	$108.96	$108.95	$109.00
Purchase #6	$45.87	7.714%	$49.4084	$49.41	$49.40	$49.40
Purchase #7	$25.88	9.243%	$28.2721	$28.27	$28.25	$28.30
7 purchase totals =	$885.89		$977.8886	$977.88	$977.85	$978.00