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	$17.31	12.299%	$19.439	$19.44	$19.45	$19.40
Purchase #2	$82.52	9.122%	$90.0475	$90.05	$90.05	$90.00
Purchase #3	$58.82	13.148%	$66.5537	$66.55	$66.55	$66.60
Purchase #4	$103.98	7.795%	$112.0852	$112.09	$112.10	$112.10
Purchase #5	$46.33	7.546%	$49.8261	$49.83	$49.85	$49.80
Purchase #6	$86.96	4.570%	$90.9341	$90.93	$90.95	$90.90
Purchase #7	$207.83	13.334%	$235.5421	$235.54	$235.55	$235.50
7 purchase totals =	$603.75		$664.4277	$664.43	$664.50	$664.30