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	$180.92	5.255%	$190.4273	$190.43	$190.45	$190.40
Purchase #2	$192.72	9.613%	$211.2462	$211.25	$211.25	$211.20
Purchase #3	$68.33	13.454%	$77.5231	$77.52	$77.50	$77.50
Purchase #4	$25.75	6.656%	$27.4639	$27.46	$27.45	$27.50
Purchase #5	$177.99	4.647%	$186.2612	$186.26	$186.25	$186.30
Purchase #6	$130.42	11.105%	$144.9031	$144.90	$144.90	$144.90
Purchase #7	$85.82	6.105%	$91.0593	$91.06	$91.05	$91.10
7 purchase totals =	$861.95		$928.8841	$928.88	$928.85	$928.90