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	$34.50	12.850%	$38.9333	$38.93	$38.95	$38.90
Purchase #2	$56.79	9.518%	$62.1953	$62.20	$62.20	$62.20
Purchase #3	$17.32	6.803%	$18.4983	$18.50	$18.50	$18.50
Purchase #4	$81.65	13.431%	$92.6164	$92.62	$92.60	$92.60
Purchase #5	$221.49	3.787%	$229.8778	$229.88	$229.90	$229.90
Purchase #6	$36.89	4.548%	$38.5678	$38.57	$38.55	$38.60
Purchase #7	$174.28	9.111%	$190.1587	$190.16	$190.15	$190.20
7 purchase totals =	$622.92		$670.8476	$670.86	$670.85	$670.90