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	$29.58	11.146%	$32.877	$32.88	$32.90	$32.90
Purchase #2	$191.84	6.113%	$203.5672	$203.57	$203.55	$203.60
Purchase #3	$105.87	7.296%	$113.5943	$113.59	$113.60	$113.60
Purchase #4	$66.87	5.672%	$70.6629	$70.66	$70.65	$70.70
Purchase #5	$40.83	7.587%	$43.9278	$43.93	$43.95	$43.90
Purchase #6	$238.76	12.477%	$268.5501	$268.55	$268.55	$268.60
Purchase #7	$34.41	11.366%	$38.321	$38.32	$38.30	$38.30
7 purchase totals =	$708.16		$771.5003	$771.50	$771.50	$771.60