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	$97.67	12.536%	$109.9139	$109.91	$109.90	$109.90
Purchase #2	$160.65	4.649%	$168.1186	$168.12	$168.10	$168.10
Purchase #3	$188.87	13.853%	$215.0342	$215.03	$215.05	$215.00
Purchase #4	$69.28	4.744%	$72.5666	$72.57	$72.55	$72.60
Purchase #5	$106.37	6.115%	$112.8745	$112.87	$112.85	$112.90
Purchase #6	$96.79	8.442%	$104.961	$104.96	$104.95	$105.00
Purchase #7	$162.44	10.157%	$178.939	$178.94	$178.95	$178.90
7 purchase totals =	$882.07		$962.4078	$962.40	$962.35	$962.40