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	$94.27	9.137%	$102.8834	$102.88	$102.90	$102.90
Purchase #2	$80.45	12.475%	$90.4861	$90.49	$90.50	$90.50
Purchase #3	$151.48	4.489%	$158.2799	$158.28	$158.30	$158.30
Purchase #4	$58.60	7.244%	$62.845	$62.85	$62.85	$62.80
Purchase #5	$95.87	6.667%	$102.2617	$102.26	$102.25	$102.30
Purchase #6	$6.43	10.850%	$7.1277	$7.13	$7.15	$7.10
Purchase #7	$66.28	7.798%	$71.4485	$71.45	$71.45	$71.40
7 purchase totals =	$553.38		$595.3323	$595.34	$595.40	$595.30