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	$215.67	6.344%	$229.3521	$229.35	$229.35	$229.40
Purchase #2	$171.42	10.223%	$188.9443	$188.94	$188.95	$188.90
Purchase #3	$123.68	3.349%	$127.822	$127.82	$127.80	$127.80
Purchase #4	$237.85	10.236%	$262.1963	$262.20	$262.20	$262.20
Purchase #5	$61.70	8.723%	$67.0821	$67.08	$67.10	$67.10
Purchase #6	$51.65	12.145%	$57.9229	$57.92	$57.90	$57.90
Purchase #7	$190.34	5.243%	$200.3195	$200.32	$200.30	$200.30
7 purchase totals =	$1,052.31		$1,133.6392	$1,133.63	$1,133.60	$1,133.60