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	$50.84	5.126%	$53.4461	$53.45	$53.45	$53.40
Purchase #2	$216.30	9.493%	$236.8334	$236.83	$236.85	$236.80
Purchase #3	$136.46	3.368%	$141.056	$141.06	$141.05	$141.10
Purchase #4	$53.27	11.314%	$59.297	$59.30	$59.30	$59.30
Purchase #5	$25.87	10.460%	$28.576	$28.58	$28.60	$28.60
Purchase #6	$148.75	13.573%	$168.9398	$168.94	$168.95	$168.90
Purchase #7	$29.71	8.704%	$32.296	$32.30	$32.30	$32.30
7 purchase totals =	$661.20		$720.4443	$720.46	$720.50	$720.40