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	$213.36	4.746%	$223.4861	$223.49	$223.50	$223.50
Purchase #2	$185.83	4.625%	$194.4246	$194.42	$194.40	$194.40
Purchase #3	$112.51	13.173%	$127.3309	$127.33	$127.35	$127.30
Purchase #4	$45.91	9.295%	$50.1773	$50.18	$50.20	$50.20
Purchase #5	$47.50	3.158%	$49.0001	$49.00	$49.00	$49.00
Purchase #6	$132.44	4.604%	$138.5375	$138.54	$138.55	$138.50
Purchase #7	$144.31	5.268%	$151.9123	$151.91	$151.90	$151.90
7 purchase totals =	$881.86		$934.8688	$934.87	$934.90	$934.80