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	$147.65	8.416%	$160.0762	$160.08	$160.10	$160.10
Purchase #2	$215.30	10.222%	$237.308	$237.31	$237.30	$237.30
Purchase #3	$208.55	7.218%	$223.6031	$223.60	$223.60	$223.60
Purchase #4	$81.48	10.190%	$89.7828	$89.78	$89.80	$89.80
Purchase #5	$27.71	4.189%	$28.8708	$28.87	$28.85	$28.90
Purchase #6	$55.69	11.702%	$62.2068	$62.21	$62.20	$62.20
Purchase #7	$106.71	12.182%	$119.7094	$119.71	$119.70	$119.70
7 purchase totals =	$843.09		$921.5571	$921.56	$921.55	$921.60