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	$30.90	5.369%	$32.559	$32.56	$32.55	$32.60
Purchase #2	$132.78	4.599%	$138.8866	$138.89	$138.90	$138.90
Purchase #3	$233.38	7.114%	$249.9827	$249.98	$250.00	$250.00
Purchase #4	$173.78	11.562%	$193.8724	$193.87	$193.85	$193.90
Purchase #5	$74.79	8.828%	$81.3925	$81.39	$81.40	$81.40
Purchase #6	$102.82	8.489%	$111.5484	$111.55	$111.55	$111.50
Purchase #7	$151.51	5.638%	$160.0521	$160.05	$160.05	$160.10
7 purchase totals =	$899.96		$968.2937	$968.29	$968.30	$968.40