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	$23.45	7.325%	$25.1677	$25.17	$25.15	$25.20
Purchase #2	$35.54	5.257%	$37.4083	$37.41	$37.40	$37.40
Purchase #3	$128.76	10.195%	$141.8871	$141.89	$141.90	$141.90
Purchase #4	$100.47	9.433%	$109.9473	$109.95	$109.95	$109.90
Purchase #5	$31.39	12.835%	$35.4189	$35.42	$35.40	$35.40
Purchase #6	$117.69	8.348%	$127.5148	$127.51	$127.50	$127.50
Purchase #7	$83.77	10.703%	$92.7359	$92.74	$92.75	$92.70
7 purchase totals =	$521.07		$570.0800	$570.09	$570.05	$570.00