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	$54.66	13.123%	$61.833	$61.83	$61.85	$61.80
Purchase #2	$56.40	8.233%	$61.0434	$61.04	$61.05	$61.00
Purchase #3	$17.81	11.177%	$19.8006	$19.80	$19.80	$19.80
Purchase #4	$169.45	3.331%	$175.0944	$175.09	$175.10	$175.10
Purchase #5	$68.86	4.503%	$71.9608	$71.96	$71.95	$72.00
Purchase #6	$40.65	11.337%	$45.2585	$45.26	$45.25	$45.30
Purchase #7	$193.60	10.511%	$213.9493	$213.95	$213.95	$213.90
7 purchase totals =	$601.43		$648.9400	$648.93	$648.95	$648.90