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	$183.55	9.255%	$200.5376	$200.54	$200.55	$200.50
Purchase #2	$48.69	7.778%	$52.4771	$52.48	$52.50	$52.50
Purchase #3	$110.42	8.346%	$119.6357	$119.64	$119.65	$119.60
Purchase #4	$180.53	5.533%	$190.5187	$190.52	$190.50	$190.50
Purchase #5	$60.37	6.680%	$64.4027	$64.40	$64.40	$64.40
Purchase #6	$104.56	10.412%	$115.4468	$115.45	$115.45	$115.40
Purchase #7	$168.39	13.113%	$190.471	$190.47	$190.45	$190.50
7 purchase totals =	$856.51		$933.4896	$933.50	$933.50	$933.40