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	$125.43	13.127%	$141.8952	$141.90	$141.90	$141.90
Purchase #2	$80.97	3.246%	$83.5983	$83.60	$83.60	$83.60
Purchase #3	$226.81	5.723%	$239.7903	$239.79	$239.80	$239.80
Purchase #4	$240.83	8.720%	$261.8304	$261.83	$261.85	$261.80
Purchase #5	$67.37	12.653%	$75.8943	$75.89	$75.90	$75.90
Purchase #6	$29.73	13.867%	$33.8527	$33.85	$33.85	$33.90
Purchase #7	$99.35	4.292%	$103.6141	$103.61	$103.60	$103.60
7 purchase totals =	$870.49		$940.4753	$940.47	$940.50	$940.50