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	$97.50	12.416%	$109.6056	$109.61	$109.60	$109.60
Purchase #2	$94.63	9.376%	$103.5025	$103.50	$103.50	$103.50
Purchase #3	$49.64	12.325%	$55.7581	$55.76	$55.75	$55.80
Purchase #4	$58.69	12.400%	$65.9676	$65.97	$65.95	$66.00
Purchase #5	$164.44	10.555%	$181.7966	$181.80	$181.80	$181.80
Purchase #6	$95.39	5.192%	$100.3426	$100.34	$100.35	$100.30
Purchase #7	$43.33	13.257%	$49.0743	$49.07	$49.05	$49.10
7 purchase totals =	$603.62		$666.0473	$666.05	$666.00	$666.10