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	$163.71	13.188%	$185.3001	$185.30	$185.30	$185.30
Purchase #2	$143.78	12.316%	$161.4879	$161.49	$161.50	$161.50
Purchase #3	$221.45	3.452%	$229.0945	$229.09	$229.10	$229.10
Purchase #4	$164.57	12.677%	$185.4325	$185.43	$185.45	$185.40
Purchase #5	$122.39	12.446%	$137.6227	$137.62	$137.60	$137.60
Purchase #6	$23.27	10.140%	$25.6296	$25.63	$25.65	$25.60
Purchase #7	$81.90	7.497%	$88.04	$88.04	$88.05	$88.00
7 purchase totals =	$921.07		$1,012.6073	$1,012.60	$1,012.65	$1,012.50