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	$35.49	10.439%	$39.1948	$39.19	$39.20	$39.20
Purchase #2	$239.64	6.181%	$254.4521	$254.45	$254.45	$254.50
Purchase #3	$179.46	11.456%	$200.0189	$200.02	$200.00	$200.00
Purchase #4	$105.55	7.287%	$113.2414	$113.24	$113.25	$113.20
Purchase #5	$122.98	9.729%	$134.9447	$134.94	$134.95	$134.90
Purchase #6	$91.98	11.824%	$102.8557	$102.86	$102.85	$102.90
Purchase #7	$56.84	4.857%	$59.6007	$59.60	$59.60	$59.60
7 purchase totals =	$831.94		$904.3083	$904.30	$904.30	$904.30