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	$81.40	10.268%	$89.7582	$89.76	$89.75	$89.80
Purchase #2	$138.45	12.150%	$155.2717	$155.27	$155.25	$155.30
Purchase #3	$231.49	5.386%	$243.9581	$243.96	$243.95	$244.00
Purchase #4	$114.52	12.722%	$129.0892	$129.09	$129.10	$129.10
Purchase #5	$51.73	5.680%	$54.6683	$54.67	$54.65	$54.70
Purchase #6	$78.64	11.726%	$87.8613	$87.86	$87.85	$87.90
Purchase #7	$85.49	5.110%	$89.8585	$89.86	$89.85	$89.90
7 purchase totals =	$781.72		$850.4653	$850.47	$850.40	$850.70