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	$83.91	6.685%	$89.5194	$89.52	$89.50	$89.50
Purchase #2	$123.35	7.524%	$132.6309	$132.63	$132.65	$132.60
Purchase #3	$67.45	9.794%	$74.0561	$74.06	$74.05	$74.10
Purchase #4	$66.94	5.782%	$70.8105	$70.81	$70.80	$70.80
Purchase #5	$84.52	3.341%	$87.3438	$87.34	$87.35	$87.30
Purchase #6	$240.39	12.310%	$269.982	$269.98	$270.00	$270.00
Purchase #7	$28.89	11.259%	$32.1427	$32.14	$32.15	$32.10
7 purchase totals =	$695.45		$756.4854	$756.48	$756.50	$756.40