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	$57.96	6.108%	$61.5002	$61.50	$61.50	$61.50
Purchase #2	$230.79	3.196%	$238.166	$238.17	$238.15	$238.20
Purchase #3	$241.58	5.586%	$255.0747	$255.07	$255.05	$255.10
Purchase #4	$247.60	9.595%	$271.3572	$271.36	$271.35	$271.40
Purchase #5	$214.57	3.615%	$222.3267	$222.33	$222.35	$222.30
Purchase #6	$20.59	9.797%	$22.6072	$22.61	$22.60	$22.60
Purchase #7	$15.79	10.552%	$17.4562	$17.46	$17.45	$17.50
7 purchase totals =	$1,028.88		$1,088.4882	$1,088.50	$1,088.45	$1,088.60