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	$95.82	3.741%	$99.4046	$99.40	$99.40	$99.40
Purchase #2	$50.86	13.352%	$57.6508	$57.65	$57.65	$57.70
Purchase #3	$45.44	7.677%	$48.9284	$48.93	$48.95	$48.90
Purchase #4	$124.73	11.799%	$139.4469	$139.45	$139.45	$139.40
Purchase #5	$10.31	11.286%	$11.4736	$11.47	$11.45	$11.50
Purchase #6	$151.76	5.129%	$159.5438	$159.54	$159.55	$159.50
Purchase #7	$101.40	10.491%	$112.0379	$112.04	$112.05	$112.00
7 purchase totals =	$580.32		$628.4860	$628.48	$628.50	$628.40