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	$132.79	4.269%	$138.4588	$138.46	$138.45	$138.50
Purchase #2	$160.90	12.533%	$181.0656	$181.07	$181.05	$181.10
Purchase #3	$81.57	5.224%	$85.8312	$85.83	$85.85	$85.80
Purchase #4	$86.54	4.535%	$90.4646	$90.46	$90.45	$90.50
Purchase #5	$93.30	13.665%	$106.0494	$106.05	$106.05	$106.00
Purchase #6	$30.90	12.324%	$34.7081	$34.71	$34.70	$34.70
Purchase #7	$35.91	6.689%	$38.312	$38.31	$38.30	$38.30
7 purchase totals =	$621.91		$674.8897	$674.89	$674.85	$674.90