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	$203.70	12.627%	$229.4212	$229.42	$229.40	$229.40
Purchase #2	$78.68	9.211%	$85.9272	$85.93	$85.95	$85.90
Purchase #3	$88.90	6.749%	$94.8999	$94.90	$94.90	$94.90
Purchase #4	$82.66	8.500%	$89.6861	$89.69	$89.70	$89.70
Purchase #5	$34.50	3.680%	$35.7696	$35.77	$35.75	$35.80
Purchase #6	$50.75	9.516%	$55.5794	$55.58	$55.60	$55.60
Purchase #7	$121.58	4.801%	$127.4171	$127.42	$127.40	$127.40
7 purchase totals =	$660.77		$718.7005	$718.71	$718.70	$718.70