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	$231.43	10.138%	$254.8924	$254.89	$254.90	$254.90
Purchase #2	$108.83	13.751%	$123.7952	$123.80	$123.80	$123.80
Purchase #3	$37.82	9.802%	$41.5271	$41.53	$41.55	$41.50
Purchase #4	$91.81	9.215%	$100.2703	$100.27	$100.25	$100.30
Purchase #5	$14.43	13.671%	$16.4027	$16.40	$16.40	$16.40
Purchase #6	$71.81	3.613%	$74.4045	$74.40	$74.40	$74.40
Purchase #7	$131.71	13.360%	$149.3065	$149.31	$149.30	$149.30
7 purchase totals =	$687.84		$760.5987	$760.60	$760.60	$760.60