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	$130.94	10.665%	$144.9048	$144.90	$144.90	$144.90
Purchase #2	$61.76	9.834%	$67.8335	$67.83	$67.85	$67.80
Purchase #3	$60.39	8.649%	$65.6131	$65.61	$65.60	$65.60
Purchase #4	$58.97	9.389%	$64.5067	$64.51	$64.50	$64.50
Purchase #5	$233.59	10.200%	$257.4162	$257.42	$257.40	$257.40
Purchase #6	$41.84	11.477%	$46.642	$46.64	$46.65	$46.60
Purchase #7	$182.49	6.377%	$194.1274	$194.13	$194.15	$194.10
7 purchase totals =	$769.98		$841.0437	$841.04	$841.05	$840.90