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	$52.31	13.734%	$59.4943	$59.49	$59.50	$59.50
Purchase #2	$180.35	6.804%	$192.621	$192.62	$192.60	$192.60
Purchase #3	$24.83	11.130%	$27.5936	$27.59	$27.60	$27.60
Purchase #4	$24.67	12.542%	$27.7641	$27.76	$27.75	$27.80
Purchase #5	$156.43	7.124%	$167.5741	$167.57	$167.55	$167.60
Purchase #6	$56.69	10.822%	$62.825	$62.83	$62.85	$62.80
Purchase #7	$123.70	7.426%	$132.886	$132.89	$132.90	$132.90
7 purchase totals =	$618.98		$670.7581	$670.75	$670.75	$670.80