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	$233.96	9.189%	$255.4586	$255.46	$255.45	$255.50
Purchase #2	$91.88	8.457%	$99.6503	$99.65	$99.65	$99.70
Purchase #3	$39.34	10.425%	$43.4412	$43.44	$43.45	$43.40
Purchase #4	$202.52	4.766%	$212.1721	$212.17	$212.15	$212.20
Purchase #5	$184.43	3.622%	$191.1101	$191.11	$191.10	$191.10
Purchase #6	$119.32	5.859%	$126.311	$126.31	$126.30	$126.30
Purchase #7	$25.64	11.756%	$28.6542	$28.65	$28.65	$28.70
7 purchase totals =	$897.09		$956.7975	$956.79	$956.75	$956.90