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	$50.81	12.169%	$56.9931	$56.99	$57.00	$57.00
Purchase #2	$15.37	12.628%	$17.3109	$17.31	$17.30	$17.30
Purchase #3	$126.61	3.824%	$131.4516	$131.45	$131.45	$131.50
Purchase #4	$85.66	7.262%	$91.8806	$91.88	$91.90	$91.90
Purchase #5	$233.41	3.624%	$241.8688	$241.87	$241.85	$241.90
Purchase #6	$174.65	12.709%	$196.8463	$196.85	$196.85	$196.80
Purchase #7	$39.96	5.175%	$42.0279	$42.03	$42.05	$42.00
7 purchase totals =	$726.47		$778.3792	$778.38	$778.40	$778.40