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	$200.97	6.247%	$213.5246	$213.52	$213.50	$213.50
Purchase #2	$47.41	13.846%	$53.9744	$53.97	$53.95	$54.00
Purchase #3	$130.47	12.395%	$146.6418	$146.64	$146.65	$146.60
Purchase #4	$81.41	6.831%	$86.9711	$86.97	$86.95	$87.00
Purchase #5	$18.52	12.685%	$20.8693	$20.87	$20.85	$20.90
Purchase #6	$163.53	5.416%	$172.3868	$172.39	$172.40	$172.40
Purchase #7	$158.89	3.504%	$164.4575	$164.46	$164.45	$164.50
7 purchase totals =	$801.20		$858.8255	$858.82	$858.75	$858.90