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	$230.48	9.148%	$251.5643	$251.56	$251.55	$251.60
Purchase #2	$226.45	6.513%	$241.1987	$241.20	$241.20	$241.20
Purchase #3	$249.25	3.138%	$257.0715	$257.07	$257.05	$257.10
Purchase #4	$156.39	7.352%	$167.8878	$167.89	$167.90	$167.90
Purchase #5	$89.77	12.268%	$100.783	$100.78	$100.80	$100.80
Purchase #6	$142.61	13.748%	$162.216	$162.22	$162.20	$162.20
Purchase #7	$227.76	9.365%	$249.0897	$249.09	$249.10	$249.10
7 purchase totals =	$1,322.71		$1,429.8110	$1,429.81	$1,429.80	$1,429.90