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	$250.59	11.691%	$279.8865	$279.89	$279.90	$279.90
Purchase #2	$158.45	6.341%	$168.4973	$168.50	$168.50	$168.50
Purchase #3	$202.54	11.405%	$225.6397	$225.64	$225.65	$225.60
Purchase #4	$53.52	4.836%	$56.1082	$56.11	$56.10	$56.10
Purchase #5	$36.34	6.864%	$38.8344	$38.83	$38.85	$38.80
Purchase #6	$136.95	11.763%	$153.0594	$153.06	$153.05	$153.10
Purchase #7	$238.56	11.329%	$265.5865	$265.59	$265.60	$265.60
7 purchase totals =	$1,076.95		$1,187.6120	$1,187.62	$1,187.65	$1,187.60