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	$50.84	8.169%	$54.9931	$54.99	$55.00	$55.00
Purchase #2	$86.78	8.807%	$94.4227	$94.42	$94.40	$94.40
Purchase #3	$133.78	12.267%	$150.1908	$150.19	$150.20	$150.20
Purchase #4	$64.51	9.530%	$70.6578	$70.66	$70.65	$70.70
Purchase #5	$130.83	9.633%	$143.4329	$143.43	$143.45	$143.40
Purchase #6	$35.89	5.570%	$37.8891	$37.89	$37.90	$37.90
Purchase #7	$130.33	6.172%	$138.374	$138.37	$138.35	$138.40
7 purchase totals =	$632.96		$689.9604	$689.95	$689.95	$690.00