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	$7.80	11.726%	$8.7146	$8.71	$8.70	$8.70
Purchase #2	$106.75	5.314%	$112.4227	$112.42	$112.40	$112.40
Purchase #3	$36.44	13.108%	$41.2166	$41.22	$41.20	$41.20
Purchase #4	$218.79	4.155%	$227.8807	$227.88	$227.90	$227.90
Purchase #5	$169.94	10.651%	$188.0403	$188.04	$188.05	$188.00
Purchase #6	$103.26	8.372%	$111.9049	$111.90	$111.90	$111.90
Purchase #7	$118.59	7.451%	$127.4261	$127.43	$127.45	$127.40
7 purchase totals =	$761.57		$817.6059	$817.60	$817.60	$817.50