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	$50.58	13.708%	$57.5135	$57.51	$57.50	$57.50
Purchase #2	$50.63	11.478%	$56.4413	$56.44	$56.45	$56.40
Purchase #3	$180.54	6.253%	$191.8292	$191.83	$191.85	$191.80
Purchase #4	$107.55	3.752%	$111.5853	$111.59	$111.60	$111.60
Purchase #5	$231.60	13.139%	$262.0299	$262.03	$262.05	$262.00
Purchase #6	$171.37	12.308%	$192.4622	$192.46	$192.45	$192.50
Purchase #7	$65.97	3.225%	$68.0975	$68.10	$68.10	$68.10
7 purchase totals =	$858.24		$939.9589	$939.96	$940.00	$939.90