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	$41.60	10.177%	$45.8336	$45.83	$45.85	$45.80
Purchase #2	$220.43	3.639%	$228.4514	$228.45	$228.45	$228.50
Purchase #3	$74.40	12.554%	$83.7402	$83.74	$83.75	$83.70
Purchase #4	$6.56	5.422%	$6.9157	$6.92	$6.90	$6.90
Purchase #5	$18.89	8.639%	$20.5219	$20.52	$20.50	$20.50
Purchase #6	$249.51	13.806%	$283.9574	$283.96	$283.95	$284.00
Purchase #7	$181.63	10.351%	$200.4305	$200.43	$200.45	$200.40
7 purchase totals =	$793.02		$869.8507	$869.85	$869.85	$869.80