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	$223.77	12.103%	$250.8529	$250.85	$250.85	$250.90
Purchase #2	$238.29	9.673%	$261.3398	$261.34	$261.35	$261.30
Purchase #3	$29.40	13.609%	$33.401	$33.40	$33.40	$33.40
Purchase #4	$35.60	13.639%	$40.4555	$40.46	$40.45	$40.50
Purchase #5	$24.27	13.194%	$27.4722	$27.47	$27.45	$27.50
Purchase #6	$88.71	10.531%	$98.0521	$98.05	$98.05	$98.10
Purchase #7	$173.53	6.287%	$184.4398	$184.44	$184.45	$184.40
7 purchase totals =	$813.57		$896.0133	$896.01	$896.00	$896.10