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	$172.59	10.341%	$190.4375	$190.44	$190.45	$190.40
Purchase #2	$46.98	5.308%	$49.4737	$49.47	$49.45	$49.50
Purchase #3	$249.55	6.493%	$265.7533	$265.75	$265.75	$265.80
Purchase #4	$184.77	8.470%	$200.42	$200.42	$200.40	$200.40
Purchase #5	$46.77	5.609%	$49.3933	$49.39	$49.40	$49.40
Purchase #6	$39.79	7.357%	$42.7174	$42.72	$42.70	$42.70
Purchase #7	$131.59	12.786%	$148.4151	$148.42	$148.40	$148.40
7 purchase totals =	$872.04		$946.6103	$946.61	$946.55	$946.60