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	$108.89	13.770%	$123.8842	$123.88	$123.90	$123.90
Purchase #2	$216.63	10.710%	$239.8311	$239.83	$239.85	$239.80
Purchase #3	$195.71	11.429%	$218.0777	$218.08	$218.10	$218.10
Purchase #4	$89.82	11.398%	$100.0577	$100.06	$100.05	$100.10
Purchase #5	$33.37	10.376%	$36.8325	$36.83	$36.85	$36.80
Purchase #6	$191.52	10.178%	$211.0129	$211.01	$211.00	$211.00
Purchase #7	$44.63	10.669%	$49.3916	$49.39	$49.40	$49.40
7 purchase totals =	$880.57		$979.0877	$979.08	$979.15	$979.10