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	$74.87	5.198%	$78.7617	$78.76	$78.75	$78.80
Purchase #2	$67.88	13.157%	$76.811	$76.81	$76.80	$76.80
Purchase #3	$144.60	6.739%	$154.3446	$154.34	$154.35	$154.30
Purchase #4	$41.43	12.181%	$46.4766	$46.48	$46.50	$46.50
Purchase #5	$137.81	12.334%	$154.8075	$154.81	$154.80	$154.80
Purchase #6	$54.72	8.770%	$59.5189	$59.52	$59.50	$59.50
Purchase #7	$36.71	12.836%	$41.4221	$41.42	$41.40	$41.40
7 purchase totals =	$558.02		$612.1424	$612.14	$612.10	$612.10