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	$167.89	6.870%	$179.424	$179.42	$179.40	$179.40
Purchase #2	$213.90	8.365%	$231.7927	$231.79	$231.80	$231.80
Purchase #3	$132.37	8.388%	$143.4732	$143.47	$143.45	$143.50
Purchase #4	$221.41	5.584%	$233.7735	$233.77	$233.75	$233.80
Purchase #5	$40.87	10.192%	$45.0355	$45.04	$45.05	$45.00
Purchase #6	$120.69	5.639%	$127.4957	$127.50	$127.50	$127.50
Purchase #7	$30.97	5.389%	$32.639	$32.64	$32.65	$32.60
7 purchase totals =	$928.10		$993.6336	$993.63	$993.60	$993.60