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	$72.84	7.658%	$78.4181	$78.42	$78.40	$78.40
Purchase #2	$41.52	3.695%	$43.0542	$43.05	$43.05	$43.10
Purchase #3	$146.31	11.187%	$162.6777	$162.68	$162.70	$162.70
Purchase #4	$9.98	12.114%	$11.189	$11.19	$11.20	$11.20
Purchase #5	$85.46	10.422%	$94.3666	$94.37	$94.35	$94.40
Purchase #6	$174.77	8.702%	$189.9785	$189.98	$190.00	$190.00
Purchase #7	$78.59	9.119%	$85.7566	$85.76	$85.75	$85.80
7 purchase totals =	$609.47		$665.4407	$665.45	$665.45	$665.60