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	$81.31	12.515%	$91.4859	$91.49	$91.50	$91.50
Purchase #2	$150.26	7.840%	$162.0404	$162.04	$162.05	$162.00
Purchase #3	$105.44	8.261%	$114.1504	$114.15	$114.15	$114.20
Purchase #4	$95.27	7.471%	$102.3876	$102.39	$102.40	$102.40
Purchase #5	$87.51	5.730%	$92.5243	$92.52	$92.50	$92.50
Purchase #6	$101.99	9.471%	$111.6495	$111.65	$111.65	$111.60
Purchase #7	$238.68	8.530%	$259.0394	$259.04	$259.05	$259.00
7 purchase totals =	$860.46		$933.2775	$933.28	$933.30	$933.20