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	$36.56	7.746%	$39.3919	$39.39	$39.40	$39.40
Purchase #2	$182.43	10.550%	$201.6764	$201.68	$201.70	$201.70
Purchase #3	$47.72	4.836%	$50.0277	$50.03	$50.05	$50.00
Purchase #4	$72.45	12.321%	$81.3766	$81.38	$81.40	$81.40
Purchase #5	$55.57	7.114%	$59.5232	$59.52	$59.50	$59.50
Purchase #6	$196.90	12.545%	$221.6011	$221.60	$221.60	$221.60
Purchase #7	$50.50	6.732%	$53.8997	$53.90	$53.90	$53.90
7 purchase totals =	$642.13		$707.4966	$707.50	$707.55	$707.50