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	$32.78	5.212%	$34.4885	$34.49	$34.50	$34.50
Purchase #2	$31.51	12.153%	$35.3394	$35.34	$35.35	$35.30
Purchase #3	$151.31	6.105%	$160.5475	$160.55	$160.55	$160.50
Purchase #4	$125.42	13.716%	$142.6226	$142.62	$142.60	$142.60
Purchase #5	$115.42	4.623%	$120.7559	$120.76	$120.75	$120.80
Purchase #6	$113.42	5.142%	$119.2521	$119.25	$119.25	$119.30
Purchase #7	$22.83	11.328%	$25.4162	$25.42	$25.40	$25.40
7 purchase totals =	$592.69		$638.4222	$638.43	$638.40	$638.40