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	$138.90	12.512%	$156.2792	$156.28	$156.30	$156.30
Purchase #2	$119.49	10.113%	$131.574	$131.57	$131.55	$131.60
Purchase #3	$177.94	5.700%	$188.0826	$188.08	$188.10	$188.10
Purchase #4	$212.45	8.662%	$230.8524	$230.85	$230.85	$230.90
Purchase #5	$87.27	4.171%	$90.91	$90.91	$90.90	$90.90
Purchase #6	$24.92	3.331%	$25.7501	$25.75	$25.75	$25.80
Purchase #7	$245.64	3.460%	$254.1391	$254.14	$254.15	$254.10
7 purchase totals =	$1,006.61		$1,077.5874	$1,077.58	$1,077.60	$1,077.70