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	$46.72	12.731%	$52.6679	$52.67	$52.65	$52.70
Purchase #2	$209.49	7.215%	$224.6047	$224.60	$224.60	$224.60
Purchase #3	$200.48	10.668%	$221.8672	$221.87	$221.85	$221.90
Purchase #4	$62.90	4.870%	$65.9632	$65.96	$65.95	$66.00
Purchase #5	$75.38	4.190%	$78.5384	$78.54	$78.55	$78.50
Purchase #6	$38.56	12.637%	$43.4328	$43.43	$43.45	$43.40
Purchase #7	$110.81	7.594%	$119.2249	$119.22	$119.20	$119.20
7 purchase totals =	$744.34		$806.2991	$806.29	$806.25	$806.30