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	$66.30	6.838%	$70.8336	$70.83	$70.85	$70.80
Purchase #2	$64.76	12.525%	$72.8712	$72.87	$72.85	$72.90
Purchase #3	$248.32	9.672%	$272.3375	$272.34	$272.35	$272.30
Purchase #4	$13.85	12.596%	$15.5945	$15.59	$15.60	$15.60
Purchase #5	$195.43	10.734%	$216.4075	$216.41	$216.40	$216.40
Purchase #6	$90.70	13.551%	$102.9908	$102.99	$103.00	$103.00
Purchase #7	$159.58	7.703%	$171.8724	$171.87	$171.85	$171.90
7 purchase totals =	$838.94		$922.9075	$922.90	$922.90	$922.90