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	$73.97	6.693%	$78.9208	$78.92	$78.90	$78.90
Purchase #2	$126.61	11.700%	$141.4234	$141.42	$141.40	$141.40
Purchase #3	$247.65	9.614%	$271.4591	$271.46	$271.45	$271.50
Purchase #4	$161.95	13.451%	$183.7339	$183.73	$183.75	$183.70
Purchase #5	$196.50	13.219%	$222.4753	$222.48	$222.50	$222.50
Purchase #6	$12.25	13.724%	$13.9312	$13.93	$13.95	$13.90
Purchase #7	$189.47	13.297%	$214.6638	$214.66	$214.65	$214.70
7 purchase totals =	$1,008.40		$1,126.6075	$1,126.60	$1,126.60	$1,126.60