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	$137.86	8.154%	$149.1011	$149.10	$149.10	$149.10
Purchase #2	$229.70	12.564%	$258.5595	$258.56	$258.55	$258.60
Purchase #3	$54.27	9.627%	$59.4946	$59.49	$59.50	$59.50
Purchase #4	$176.97	13.444%	$200.7618	$200.76	$200.75	$200.80
Purchase #5	$39.60	4.631%	$41.4339	$41.43	$41.45	$41.40
Purchase #6	$69.36	4.206%	$72.2773	$72.28	$72.30	$72.30
Purchase #7	$142.75	3.293%	$147.4508	$147.45	$147.45	$147.50
7 purchase totals =	$850.51		$929.0790	$929.07	$929.10	$929.20