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	$34.49	11.226%	$38.3618	$38.36	$38.35	$38.40
Purchase #2	$164.36	3.351%	$169.8677	$169.87	$169.85	$169.90
Purchase #3	$200.97	9.198%	$219.4552	$219.46	$219.45	$219.50
Purchase #4	$78.60	5.826%	$83.1792	$83.18	$83.20	$83.20
Purchase #5	$160.59	4.503%	$167.8214	$167.82	$167.80	$167.80
Purchase #6	$28.82	11.854%	$32.2363	$32.24	$32.25	$32.20
Purchase #7	$152.83	3.698%	$158.4817	$158.48	$158.50	$158.50
7 purchase totals =	$820.66		$869.4033	$869.41	$869.40	$869.50