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	$237.65	13.808%	$270.4647	$270.46	$270.45	$270.50
Purchase #2	$128.30	13.280%	$145.3382	$145.34	$145.35	$145.30
Purchase #3	$90.48	13.186%	$102.4107	$102.41	$102.40	$102.40
Purchase #4	$129.32	11.223%	$143.8336	$143.83	$143.85	$143.80
Purchase #5	$117.47	12.565%	$132.2301	$132.23	$132.25	$132.20
Purchase #6	$63.35	4.417%	$66.1482	$66.15	$66.15	$66.10
Purchase #7	$190.83	7.759%	$205.6365	$205.64	$205.65	$205.60
7 purchase totals =	$957.40		$1,066.0620	$1,066.06	$1,066.10	$1,065.90