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	$56.57	6.133%	$60.0394	$60.04	$60.05	$60.00
Purchase #2	$87.51	10.244%	$96.4745	$96.47	$96.45	$96.50
Purchase #3	$139.67	13.495%	$158.5185	$158.52	$158.50	$158.50
Purchase #4	$245.79	9.755%	$269.7668	$269.77	$269.75	$269.80
Purchase #5	$230.32	7.223%	$246.956	$246.96	$246.95	$247.00
Purchase #6	$46.88	10.851%	$51.9669	$51.97	$51.95	$52.00
Purchase #7	$82.61	9.676%	$90.6033	$90.60	$90.60	$90.60
7 purchase totals =	$889.35		$974.3254	$974.33	$974.25	$974.40