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	$247.27	13.569%	$280.8221	$280.82	$280.80	$280.80
Purchase #2	$147.51	11.328%	$164.2199	$164.22	$164.20	$164.20
Purchase #3	$238.95	7.583%	$257.0696	$257.07	$257.05	$257.10
Purchase #4	$250.63	3.716%	$259.9434	$259.94	$259.95	$259.90
Purchase #5	$194.86	10.498%	$215.3164	$215.32	$215.30	$215.30
Purchase #6	$231.82	3.694%	$240.3834	$240.38	$240.40	$240.40
Purchase #7	$98.80	5.148%	$103.8862	$103.89	$103.90	$103.90
7 purchase totals =	$1,409.84		$1,521.6410	$1,521.64	$1,521.60	$1,521.60