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	$83.35	7.252%	$89.3945	$89.39	$89.40	$89.40
Purchase #2	$52.29	4.156%	$54.4632	$54.46	$54.45	$54.50
Purchase #3	$145.45	7.357%	$156.1508	$156.15	$156.15	$156.20
Purchase #4	$39.84	9.446%	$43.6033	$43.60	$43.60	$43.60
Purchase #5	$174.53	8.547%	$189.4471	$189.45	$189.45	$189.40
Purchase #6	$199.75	6.676%	$213.0853	$213.09	$213.10	$213.10
Purchase #7	$221.74	5.122%	$233.0975	$233.10	$233.10	$233.10
7 purchase totals =	$916.95		$979.2417	$979.24	$979.25	$979.30