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	$186.81	12.162%	$209.5298	$209.53	$209.55	$209.50
Purchase #2	$177.47	3.646%	$183.9406	$183.94	$183.95	$183.90
Purchase #3	$231.91	4.362%	$242.0259	$242.03	$242.05	$242.00
Purchase #4	$218.76	13.614%	$248.542	$248.54	$248.55	$248.50
Purchase #5	$89.63	12.388%	$100.7334	$100.73	$100.75	$100.70
Purchase #6	$244.79	5.541%	$258.3538	$258.35	$258.35	$258.40
Purchase #7	$90.82	10.743%	$100.5768	$100.58	$100.60	$100.60
7 purchase totals =	$1,240.19		$1,343.7023	$1,343.70	$1,343.80	$1,343.60