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	$227.79	12.783%	$256.9084	$256.91	$256.90	$256.90
Purchase #2	$44.47	6.563%	$47.3886	$47.39	$47.40	$47.40
Purchase #3	$154.74	3.594%	$160.3014	$160.30	$160.30	$160.30
Purchase #4	$151.74	10.160%	$167.1568	$167.16	$167.15	$167.20
Purchase #5	$215.78	11.232%	$240.0164	$240.02	$240.00	$240.00
Purchase #6	$39.42	10.167%	$43.4278	$43.43	$43.45	$43.40
Purchase #7	$180.88	13.236%	$204.8213	$204.82	$204.80	$204.80
7 purchase totals =	$1,014.82		$1,120.0207	$1,120.03	$1,120.00	$1,120.00