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	$113.83	3.385%	$117.6831	$117.68	$117.70	$117.70
Purchase #2	$124.54	12.103%	$139.6131	$139.61	$139.60	$139.60
Purchase #3	$71.56	12.793%	$80.7147	$80.71	$80.70	$80.70
Purchase #4	$48.51	12.409%	$54.5296	$54.53	$54.55	$54.50
Purchase #5	$183.47	12.759%	$206.8789	$206.88	$206.90	$206.90
Purchase #6	$43.86	12.511%	$49.3473	$49.35	$49.35	$49.30
Purchase #7	$155.77	11.629%	$173.8845	$173.88	$173.90	$173.90
7 purchase totals =	$741.54		$822.6512	$822.64	$822.70	$822.60