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	$25.30	8.182%	$27.37	$27.37	$27.35	$27.40
Purchase #2	$130.40	9.191%	$142.3851	$142.39	$142.40	$142.40
Purchase #3	$134.60	7.491%	$144.6829	$144.68	$144.70	$144.70
Purchase #4	$142.83	6.435%	$152.0211	$152.02	$152.00	$152.00
Purchase #5	$199.43	6.812%	$213.0152	$213.02	$213.00	$213.00
Purchase #6	$82.40	5.498%	$86.9304	$86.93	$86.95	$86.90
Purchase #7	$128.32	9.446%	$140.4411	$140.44	$140.45	$140.40
7 purchase totals =	$843.28		$906.8458	$906.85	$906.85	$906.80