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	$117.37	12.398%	$131.9215	$131.92	$131.90	$131.90
Purchase #2	$221.62	4.828%	$232.3198	$232.32	$232.30	$232.30
Purchase #3	$226.44	5.594%	$239.1071	$239.11	$239.10	$239.10
Purchase #4	$78.71	9.847%	$86.4606	$86.46	$86.45	$86.50
Purchase #5	$172.87	8.226%	$187.0903	$187.09	$187.10	$187.10
Purchase #6	$87.81	4.583%	$91.8343	$91.83	$91.85	$91.80
Purchase #7	$114.37	11.721%	$127.7753	$127.78	$127.80	$127.80
7 purchase totals =	$1,019.19		$1,096.5089	$1,096.51	$1,096.50	$1,096.50