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	$230.78	10.560%	$255.1504	$255.15	$255.15	$255.20
Purchase #2	$155.65	4.866%	$163.2239	$163.22	$163.20	$163.20
Purchase #3	$140.27	7.236%	$150.4199	$150.42	$150.40	$150.40
Purchase #4	$240.48	13.573%	$273.1204	$273.12	$273.10	$273.10
Purchase #5	$40.51	7.799%	$43.6694	$43.67	$43.65	$43.70
Purchase #6	$35.35	6.136%	$37.5191	$37.52	$37.50	$37.50
Purchase #7	$160.78	7.819%	$173.3514	$173.35	$173.35	$173.40
7 purchase totals =	$1,003.82		$1,096.4545	$1,096.45	$1,096.35	$1,096.50