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	$133.76	8.811%	$145.5456	$145.55	$145.55	$145.50
Purchase #2	$90.54	6.384%	$96.3201	$96.32	$96.30	$96.30
Purchase #3	$132.40	9.868%	$145.4652	$145.47	$145.45	$145.50
Purchase #4	$50.61	11.277%	$56.3173	$56.32	$56.30	$56.30
Purchase #5	$250.91	8.254%	$271.6201	$271.62	$271.60	$271.60
Purchase #6	$76.98	11.417%	$85.7688	$85.77	$85.75	$85.80
Purchase #7	$176.27	4.224%	$183.7156	$183.72	$183.70	$183.70
7 purchase totals =	$911.47		$984.7527	$984.77	$984.65	$984.70