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	$5.46	9.587%	$5.9835	$5.98	$6.00	$6.00
Purchase #2	$115.77	6.575%	$123.3819	$123.38	$123.40	$123.40
Purchase #3	$59.93	4.205%	$62.4501	$62.45	$62.45	$62.50
Purchase #4	$79.60	12.791%	$89.7816	$89.78	$89.80	$89.80
Purchase #5	$36.77	8.805%	$40.0076	$40.01	$40.00	$40.00
Purchase #6	$141.31	6.721%	$150.8074	$150.81	$150.80	$150.80
Purchase #7	$178.59	11.538%	$199.1957	$199.20	$199.20	$199.20
7 purchase totals =	$617.43		$671.6078	$671.61	$671.65	$671.70