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	$225.40	5.744%	$238.347	$238.35	$238.35	$238.30
Purchase #2	$54.76	9.517%	$59.9715	$59.97	$59.95	$60.00
Purchase #3	$242.89	4.119%	$252.8946	$252.89	$252.90	$252.90
Purchase #4	$33.91	3.474%	$35.088	$35.09	$35.10	$35.10
Purchase #5	$53.27	11.652%	$59.477	$59.48	$59.50	$59.50
Purchase #6	$113.40	12.189%	$127.2223	$127.22	$127.20	$127.20
Purchase #7	$137.69	4.501%	$143.8874	$143.89	$143.90	$143.90
7 purchase totals =	$861.32		$916.8878	$916.89	$916.90	$916.90