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	$80.75	12.478%	$90.826	$90.83	$90.85	$90.80
Purchase #2	$211.33	6.385%	$224.8234	$224.82	$224.80	$224.80
Purchase #3	$191.60	6.287%	$203.6459	$203.65	$203.65	$203.60
Purchase #4	$123.94	10.609%	$137.0888	$137.09	$137.10	$137.10
Purchase #5	$225.37	7.189%	$241.5718	$241.57	$241.55	$241.60
Purchase #6	$233.54	12.312%	$262.2934	$262.29	$262.30	$262.30
Purchase #7	$37.32	8.403%	$40.456	$40.46	$40.45	$40.50
7 purchase totals =	$1,103.85		$1,200.7053	$1,200.71	$1,200.70	$1,200.70